The maths, explained
Measure the paintable surface, enter the number of coats, and take coverage from the selected product’s technical information. The model divides total coat area by coverage per litre and adds your allowance. In imperial mode the same coverage is displayed as square feet per US gallon; conversion preserves the underlying physical rate. It does not round to available tins or cans.
Paint litres = area × coats ÷ coverage × (1 + waste / 100)
A worked example
The worked example below uses the calculator’s initial inputs and the same calculation function as the live interface. Replace example amounts with your own records; changing currency does not convert the numbers. Physical reference dimensions are stored in metric units, and the interface can display their imperial equivalents. Rounded display values may differ slightly from the full precision retained in the calculation.
| Your inputs | Editable example — not a market quote |
|---|---|
| Paintable area | 645.834625 sq ft |
| Number of coats | 2 |
| Coverage per litre | 407.458333 sq ft/US gal |
| Order quantity with 10% example waste | 3.49 US gal |
Assumptions used
The result assumes simple geometry and the dimensions actually entered. Waste, unit price and allowances are editable assumptions, not verified regional market rates. An allowance is not a guarantee: compare the answer with the chosen product, cutting or laying plan, and delivery constraints. Tax is applied to the complete subtotal including contingency in this model; adjust the budget if your applicable tax base differs.
On your side of the Atlantic
Use your state and local sales-tax treatment, payroll records, and supplier quotes. A national default cannot describe every US job.
Common mistakes
Do not treat advertised coverage as guaranteed on every substrate. Primer, texture, absorption, colour changes and application method can alter consumption. Keep coverage and volume units matched, especially US versus imperial gallons.
Before ordering or tendering, compare at least two scenarios: your base takeoff and a realistic alternative. Keep assumptions with the result so differences are explainable. Save an estimate only on a suitable device. A shared link contains the entered values, so avoid including confidential information. An exported estimate is a snapshot and does not update when a supplier changes a price.
Questions from the jobsite
What does this calculator measure?
What is the first mistake to avoid?
Are the example prices supplier quotes?
Which tax assumptions apply in United States?
How should I handle waste and contingency?
Can I use the result in a tender or estimate?
Planning estimate only. Not a substitute for a professional quote or local building-code compliance. Verify quantities, tax treatment and contract requirements.
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