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Estimate paint quantities from your supplied wall measurements

Check net area, coats and coverage, then choose whole packs that fit a stated budget.

Illustrative resourceNot tool-testedPeople planning an ordinary decorating purchase from known dimensions and product information

What you’re working towards

A source-linked area worksheet and whole-pack shopping list, with explicit supplied assumptions, budget checks and a reusable blank worksheet. It is an estimate to review before buying, not wall preparation or application advice.

Download playbook .md

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Included example · illustrative CSV file

Download the example shopping list

Static whole-pack answer with exact quantities and integer-cent line totals, including zero for the unused pack.

Not tool-tested. Review and adapt before using it for a real project. Your browser may download this file when you choose View example file.

View example file Download example

Four synthetic wall faces are each 2,400 mm high. W1 and W3 are 4,200 mm wide; W2 and W4 are 3,600 mm wide. A 1,200 by 1,000 mm window is deducted from W1 and an 800 by 2,000 mm door from W2. W3 and W4 have no supplied openings. Gross area 37.44 m² minus 2.8 m² openings gives 34.64 m² net before coats and allowance. — Owned measured diagram from the supplied synthetic input. Only the two named openings are subtracted; this is not a physical measurement or photograph.

Source files to work with

Download the complete synthetic input
All measurements, exclusions, fictional pack prices, budget and tie-break rules before the answer.
Download the structured input
Exact millimetres, opening positions, product assumptions and fictional catalogue.
Download the area worksheet
Four source-linked wall rows and the two named opening deductions.
Download the worked calculation
Exact area, volume, shopping and tie-break explanation, with real-use checks still open.
Download the checked answer values (spoilers)
Exact independent control values for this authored arithmetic example.
Download a blank worksheet for your room
Reusable unfilled measurement, assumptions, calculation and pre-purchase review fields. It does not recalculate itself.
Download the editable wall-area diagram
Owned, self-contained front-facing wall diagrams with the two supplied openings.
Download the wall-area image
1280 × 920 actual render of the owned diagram. It illustrates supplied dimensions, not a real room.

Before you begin

Known wall and opening dimensions with consistent units and included/excluded surfaces
Supplied product coverage, required coat count and an owner-chosen allowance
Known compatible pack sizes, final prices, currency and a budget
A separate real-world check of measurements, product suitability, prices and stock before purchasing

Possible tools

A text AI assistantUser-chosen paste-text interface · required
Access and plan limits unverified
No provider, account entitlement, free tier or receiving application was verified. Use a tool you already have access to. No real product label, current price or stock was checked.
An independent arithmetic checkerUser-chosen exact calculator or local script · required
Access and plan limits unverified
No provider, account entitlement, free tier or receiving application was verified. Use a tool you already have access to. No real product label, current price or stock was checked.
A text or CSV viewerUser-chosen local viewer · suggested
Access and plan limits unverified
No provider, account entitlement, free tier or receiving application was verified. Use a tool you already have access to. No real product label, current price or stock was checked.

Use the sample first. Remove private information before taking a prompt into another tool.

Make a start

One step at a time.

4 steps

Start with the synthetic worked example or other non-sensitive inputs. Run one prompt at a time in your chosen AI tool. Replace any bracketed placeholders with the requested material, check each reply, and supply the source or earlier outputs that step needs. Paste them again if the tool lacks that context.

Set up the worked example

Open: Open a fresh text-AI chat, a plain-text editor and a calculator that preserves exact decimals or fractions. Keep this guide beside them. This exercise uses rectangular wall faces and rectangular openings. A CSV is a text table here, not a calculator; no file upload is needed.
Add the sample: Download and open paint-estimate-source.md, or copy all of “The starting point” (Synthetic input). Replace step 1’s [paste] with that entire source, including exclusions, opening positions, pack rules and limits. Send one step at a time in the same chat. In step 2 paste the full checked source from step 1; in step 3 paste its complete catalogue, budget, tie-break order and step 2’s exact target. Save the source-linked area calculation and pack comparison as my-paint-estimate.txt and reopen it. In step 4’s SOURCE field paste the original source; in ESTIMATE paste your reopened calculation and pack comparison. “The intended result” (Illustrative output), answer JSON, worked CSVs and diagram are comparison answers, not measurements or your AI’s work. For the optional advanced sample exercise paste the entire original source and only the explicit practice changes you choose, such as changing the budget to USD 55.00 with everything else unchanged. Keep that scenario separate. A new chat needs the complete source and changes again.

Start with the synthetic example, then adapt each prompt to your task.

Write down the measurements and assumptions first

Start with the blank worksheet. Give each wall and opening an ID, keep the original unit, and state what is excluded. Record coverage and coats from your chosen product instead of asking the AI to guess them.

Your starting prompt

Organize this supplied paint-planning input without calculating a purchase yet. List every wall, opening, unit, included/excluded surface, coat count, product coverage and its units, allowance, compatible pack size, final price and budget. Preserve the original values and their source. Identify missing, contradictory, negative or zero-required inputs and hold the purchase calculation until resolved. Check that openings belong to known walls, fit within them and do not overlap. Do not invent product suitability, wall condition, coverage, price, stock or preparation advice.

INPUT:
[paste]

Expect: A checked list of four walls, two linked openings and all supplied calculation and pack-selection rules, before choosing packs.
Check: W1/W3 are 4,200 × 2,400 mm; W2/W4 are 3,600 × 2,400 mm. O1 belongs to W1 and O2 to W2. Check each opening’s supplied bottom-left position and far edges against its wall. Only these openings are deducted; ceiling and trim are excluded.
If it differs: If a value or rule is missing, compare with the full source and request a corrected list. Unknown coverage, units, dimensions, pack price or budget holds the affected calculation. Do not turn an empty value into zero or ask for invented product advice.

Calculate the area and volume without early rounding

The example has 37.44 m² gross wall area and 2.8 m² of named openings. After two supplied coats, 10% allowance and 10 m²/L coverage, the exact planning target is 7.6208 L.

Your starting prompt

Use the validated source to calculate each wall’s gross area, named opening deductions and net area. Show the unit conversion explicitly: mm² to m² divides by 1,000,000. Deduct only supplied, nonoverlapping openings, once each. Sum net area, multiply by the stated coats, apply the stated percentage allowance, then divide by the stated coverage with compatible units. Keep exact fractions or exact decimals throughout; do not round intermediate results or substitute assumptions. Return a source-linked area table and the exact volume target.

VALIDATED SOURCE:
[paste]

Expect: An exact area table, followed by coats, allowance and the volume target.
Check: Divide mm² by 1,000,000. Net rows are W1 8.88, W2 7.04, W3 10.08 and W4 8.64 m². On your calculator check (37.44 − 2.8) × 2 × 1.10 ÷ 10 = 7.6208 L. Preserve this target without rounding it down.
If it differs: If a row differs, recalculate its width × height and named deduction before summing. Ask for the corrected whole calculation. Do not patch only the final target while leaving a wrong area or unit conversion behind.

Compare whole packs under your actual rules

The example has two $58 combinations. The rule prefers less spare volume before fewer packs, so three 1 L packs and one 5 L pack win: 8 L. Keep the tie-break visible rather than silently preferring a neater shopping list.

Your starting prompt

Using only the supplied compatible pack catalogue, enumerate whole-pack combinations meeting the exact volume target and budget. Minimize price, then volume above the target, then number of packs, then counts in the supplied pack-ID order. Show quantities including zero for unused options, line volume and cost, total volume, total cost and budget remainder. If no combination qualifies, say no fit and identify the constraint; do not raise the budget or lower the target. Distinguish arithmetic spare capacity from observed leftover paint and do not claim measured savings.

SOURCE CATALOGUE, BUDGET AND EXACT TARGET:
[paste]

Expect: A whole-pack comparison with quantities for P1/P2/P3, exact volume, price, spare capacity and budget remainder. Save it with the area calculation in my-paint-estimate.txt.
Check: The sample choice is 3/0/1: 8 L for USD 58.00, 0.3792 L above target and USD 2.00 below budget. 1/1/1 also costs USD 58.00 but supplies 8.5 L. Less spare volume wins before fewer packs. Independently enumerate P1 counts 0–6, P2 0–3 and P3 0–1, rejecting over-budget or under-target combinations.
If it differs: If the full price/tie-break comparison was not performed, keep “minimum unverified” rather than accepting a plausible shopping list. Correct quantities and all totals together. At a USD 55.00 budget report no fit; do not lower the target or raise the budget.

Check the maths, then check the real product

Recalculate independently. The reusable worksheet is blank, and the worked CSV is a static answer rather than a live calculator. Real surfaces, labels, fees and stock still need checking before purchase.

Your starting prompt

Audit this estimate against the complete original source. Check each wall/opening once, unit conversion, coat and allowance order, exact coverage division, every pack quantity, the full price comparison and tie-break, and the budget. Test a missing coverage value, overlapping opening, wrong unit conversion, early rounding, a same-price but wrong tie-break and a budget with no feasible pack combination. Separate passed arithmetic checks from unperformed physical measurements, product/price/stock verification, painting trials and consumer-AI execution. List real-world facts still to confirm before buying.

SOURCE:
[paste]

ESTIMATE:
[paste]

Expect: An audit of your saved estimate, with separate test cases and unresolved real-use facts.
Check: Use disposable copies for tests: remove coverage; duplicate O1 under a new ID at the same coordinates; divide mm² by 1,000; round the target to 7.62; select 1/1/1 at the price tie; reduce budget to USD 55.00. Expect holds for invalid input, correction of arithmetic/tie-break errors and no fit for the lower budget. The original source must stay unchanged.
If it differs: If a test is only described, label it not run. Keep a failed version, correct a new revision, reopen it and repeat the affected checks. Before any real purchase, remeasure and verify labels, coats, coverage, compatibility, all fees, final prices and stock. Arithmetic spare capacity is not observed leftover paint.

Optional: improve the result

Show which supplied assumption changes the purchase

Keep the original source and create a separate scenario for any changed coat count, coverage, allowance, catalogue or budget. Compare complete recalculations rather than adjusting the old shopping list by intuition.

Advanced prompt

Create a separate scenario comparison from the unchanged original source. Apply only the explicitly supplied changes below, validate them and recompute the full area/volume/pack calculation exactly. Return original and revised target, chosen pack counts, price and any no-fit result. Identify the changed assumptions that explain the difference. Do not overwrite the original measurements, infer product performance, or call the price difference realized savings.

ORIGINAL SOURCE:
[paste]

EXPLICIT SCENARIO CHANGES:
[paste]

Optional: use your own input

Estimate from your own supplied measurements

Use only permitted, non-sensitive measurements and product text; omit addresses. Copy paint-estimate-blank.md into my-paint-source.txt and fill it from your own sources, adding your pack-selection tie-break order. This route supports rectangular faces/openings, compatible packs with positive known all-in prices and one currency. Start a new chat with the prompt below. Review its source table before sending each follow-up, replacing each bracketed instruction with the requested material.
“Calculate each rectangular wall’s gross area, linked opening deductions and net area from MY CHECKED SOURCE. Convert the actual supplied units explicitly, deduct each in-bounds nonoverlapping opening once, then apply my coat count, allowance order and coverage. Keep exact values. Return source-linked rows and the exact volume target. MY CHECKED SOURCE: [paste the complete reviewed source, including exclusions, units and rules].”
Check each area and conversion yourself. Resolve errors against the original measurements, then send:
“Using MY CATALOGUE, BUDGET, EXACT TARGET AND SELECTION RULES, compare all whole-pack combinations within the supplied budget and any confirmed stock limits. Show quantities including zero, line costs/volumes, totals and spare capacity. Follow my price and tie-break order exactly. Return no fit only with a complete comparison or sound constraint proof; otherwise mark the search unverified. Hold unknown fees, stock needed for a stock-constrained choice or incompatible products. Do not buy anything. CATALOGUE, BUDGET, EXACT TARGET AND RULES: [paste].”
Independently check the allowed combination range and ranking. Save your source-linked calculation and comparison as my-paint-estimate.txt, then reopen it.
“Audit MY SAVED ESTIMATE against MY ORIGINAL SOURCE. Recalculate areas, unit conversions, coat/allowance/coverage order, target and all pack totals; check every selection rule and budget. On separate copies test one missing required value, an invalid opening and a constraint failure relevant to my source. State which checks actually ran; keep unresolved product, measurement, price, fee and stock facts visible. ORIGINAL SOURCE AND REOPENED ESTIMATE: [paste both in full].”
Correct and reopen a new revision before repeating a failed check. Your measurements and prices replace every sample number. The original advanced prompt is sample-scoped; for your own separate scenario supply your full original source, explicit changed inputs and confirmation of unchanged assumptions. Actual product suitability and consumption need real checks before any separate purchase decision.

Your own-input prompt

Help me prepare a supplied-data paint quantity and whole-pack estimate, not painting instructions or a purchase decision. First organize my complete input without calculating: source-linked wall/opening IDs, rectangular dimensions and positions, units, included/excluded surfaces, product and compatibility, required coats, coverage with units/source, owner-chosen allowance and order, pack IDs/sizes/positive final prices, currency, budget, stock limits if confirmed, and my selection/tie-break order. Check unique IDs, positive required dimensions/coats/coverage/pack sizes/prices, nonnegative allowance/budget, opening containment and overlap. Hold missing, invalid, contradictory or unsupported inputs, including unclear units or nonrectangular geometry. Unknown fees are not zero. Preserve the original and stop for my review. Later we will calculate exact area/volume, compare whole packs, save and independently audit the estimate. Do not buy, contact anyone, infer product performance or claim real measurements.

MY COMPLETE MEASUREMENT AND PRODUCT SOURCE
[Paste your completed worksheet and relevant label/catalogue text, including every input listed above. Say which prices are confirmed all-in, which stock limits are known and which facts remain unknown. State your exact optimization and tie-break order.]

Check your own result

Each of your walls/openings is counted once; opening positions, geometry and conversion factors match your actual units.
Your supplied coats, allowance and coverage determine an unrounded target; the sample target and pack counts are not a template answer.
Every considered pack is compatible and priced on the same confirmed basis; your budget, stock limits and tie-break rules stay intact.
Unknown required facts hold the relevant calculation, and a no-fit or unverified search is never presented as a confirmed purchase choice.
Reopened saved results agree with their complete source. Actual labels, suitability, measurements, fees, prices and stock still need confirmation; spare capacity is not observed leftover paint.

Show, then try

See the shape of the result.

This input is synthetic. The output is a written illustration of the intended result, not a verified AI-tool run.

The starting point

Synthetic input

# Paint shopping estimate: complete synthetic input

Use these supplied values to make a checkable shopping estimate, not painting instructions or a real product quote. All dimensions, rates and prices are invented. There are no real addresses or people.

## Wall faces and openings

All measurements are in millimetres. Every wall is 2,400 mm high. W1 and W3 are 4,200 mm wide; W2 and W4 are 3,600 mm wide. Include each wall once. Exclude ceiling, trim and every other surface.

- O1: a 1,200 × 1,000 mm window on W1, with bottom-left coordinate (1,500, 900).
- O2: an 800 × 2,000 mm door on W2, with bottom-left coordinate (500, 0).

Subtract only these two openings, once each. Coordinates start at the bottom-left of their own wall. Reject openings outside a wall or overlapping another opening; do not double-subtract.

## Planning assumptions supplied by the owner

- Coats: 2.
- Coverage: 10 square metres per litre for this fictional product.
- Allowance: add 10% after multiplying the net area by the coat count.
- Currency: USD. Budget: $60.00.
- P1: 1,000 mL pack, $9.00.
- P2: 2,500 mL pack, $18.00.
- P3: 5,000 mL pack, $31.00.

For this arithmetic fixture, all packs contain the same compatible product/finish and the prices are fictional all-in amounts. No additional fee exists in the fixture. Real suitability, compatibility, taxes, delivery, stock and current prices are unverified.

## Required result

Show each wall's gross area, its linked opening deductions and net area. Convert mm² to m² explicitly. Multiply total net area by coats, apply the supplied allowance, then divide by coverage, keeping exact values throughout.

Choose whole packs that meet the planning target and stay within budget. Minimize price. Break equal-price ties by less volume above target, fewer packs, then the counts in P1/P2/P3 order. Show quantities, total volume, total price and volume above the planning target. If no combination fits, report no fit rather than weakening a constraint.

Hold the purchase calculation if required dimensions, units, coats, coverage, pack sizes/prices or budget are missing or invalid. Do not infer a coverage rate, add an unsupplied opening or turn unknown into zero.

## Real-use decisions still required

This is not painting or preparation advice. Remeasure the real surfaces and openings. Verify the chosen product label, coverage, required coats, finish compatibility, available pack sizes, final prices and stock before buying. Wall condition and actual consumption were not assessed. The 10% allowance is a supplied planning choice, not a guarantee. Volume above target is arithmetic spare capacity, not observed leftover paint.

Copies text only. For image or file tasks, use the source files named in the steps too.

Download source .txt

The intended result

Illustrative output

# A checked paint shopping estimate

For this fictional input, the lowest-price allowed combination is three P1 packs and one P3 pack: four packs, 8 L and $58.00 in total. It meets the 7.6208 L planning target and the $60.00 budget. This is an illustrative arithmetic answer, not a real quotation or a purchase recommendation.

## Area and target, without intermediate rounding

- Gross wall area: 10.08 + 8.64 + 10.08 + 8.64 = 37.44 m².
- Openings: 1.2 m² on W1 and 1.6 m² on W2, total 2.8 m².
- Net wall area: 37.44 − 2.8 = 34.64 m².
- Two coats: 34.64 × 2 = 69.28 m².
- Supplied 10% allowance: 69.28 × 1.10 = 76.208 m².
- Supplied 10 m²/L coverage: 76.208 ÷ 10 = 7.6208 L.

One square metre is 1,000,000 square millimetres. The source dimensions are converted by area, not by dividing mm² by 1,000. Only the two named, nonoverlapping in-bounds openings are deducted.

## Example shopping list

| Pack | Quantity | Supplied size | Supplied price |
|---|---:|---:|---:|
| P1 | 3 | 1 L | $9.00 each |
| P2 | 0 | 2.5 L | $18.00 each |
| P3 | 1 | 5 L | $31.00 each |

Total volume is 8 L; total price is $58.00. The volume above the planning target is 8 − 7.6208 = 0.3792 L, and $2.00 of the supplied budget remains. These are calculated amounts, not observed leftovers or measured savings.

Within this three-pack catalogue, positive prices let us enumerate every combination costing no more than the $60.00 budget. The accepted answer minimizes price, then spare volume, then pack count, then P1/P2/P3 counts. One of each pack also costs $58.00 but supplies 8.5 L, so the less-spare-volume tie-break chooses 8 L even though it uses four packs. Two 5 L packs meet the volume target but cost $62.00, so they fail this budget. A $55.00 budget has no feasible combination in the supplied catalogue.

## Before buying for a real room

Remeasure the surfaces/openings and verify the actual product's labelled coverage, required coats, finish compatibility, sizes, final prices and stock. Replace the entire source and recalculate when any assumption changes. Do not reinterpret this allowance as a guarantee about absorption or waste. Wall condition, preparation, product suitability, real cost and actual consumption have not been assessed. No consumer AI workflow or real purchase was performed; time savings are unmeasured.

Download result .txt

You’re the final check

Check the worked example.

These checks use the worked example and its particular facts. With your own material, check your actual names, numbers, sources and rules; do not reuse the sample’s values as the answer.

Each wall is counted once; O1 and O2 are the only opening deductions and are in bounds without overlap.The exact net area is 34.64 m² and the exact planning target is 7.6208 L.Three P1 packs, zero P2 packs and one P3 pack provide 8 L for $58.00; the budget remainder is $2.00.The same-price 8.5 L combination loses under the stated less-spare-volume tie-break, even though it uses fewer packs.A $55.00 budget has no feasible combination in this catalogue; unknown coverage is held rather than guessed.Actual wall condition, product suitability, price/stock and consumption remain unverified; spare volume is not observed leftover paint.

Unsaved checks stay in this tab and reset when you reload. If you choose Save guide, its current example checkmarks are kept in this browser when storage is available.

A few things to watch for.

Dividing square millimetres by 1,000 instead of 1,000,000.
Deducting an opening twice, inventing a window or counting trim/ceilings excluded by the source.
Guessing a coverage rate or interpreting an allowance as a guarantee about absorption.
Rounding the target down before choosing whole packs.
Choosing a same-price answer that ignores the supplied tie-break order.
Treating an illustrative shopping estimate as a real quote, painting instruction or measured saving.