Paint Calculator
Paint calculator works out Paint needed and Net paintable area from What to work out, Area unit and How the area is given. The default figures on this page give paint needed of 20.00 L; change any entry and the result, the working and the sources update together.
Your figures
Updates as you typeHow this is worked out
1 step
- Paint = 100 m2 x 2 coat(s) / 10 m2 per litre x (1 + 0/100) = 20 L
Its 5 worked examples are re-run on every release, last on 15 September 2026. What changed
Sources and references
5 sources
Keep this result
Save it, change one figure, then compare the two
The calculation stays free. Save this scenario, adjust one assumption, save that too, and put them side by side to see exactly what the change costs you. A free account keeps 5 scenarios and 2 comparisons; Personal makes both unlimited and adds exports and private links. Nothing is saved unless you press Save.
What the paint calculator calculates
Works out how much paint a job needs from the net paintable area (or room dimensions), the number of coats, the product coverage rate and a waste allowance, then converts that into tins, litres, US gallons and an installed cost.
How to use this paint calculator
Enter What to work out, Area unit, How the area is given and Net paintable area. Paint needed updates as you type, and “Use a worked example” loads checked figures you can adjust. Change one figure at a time to see what drives the result.
How the result is worked out
Open “How this is worked out” beside the result for the step-by-step calculation behind Paint needed, Net paintable area and Coverage rate used.
The method follows 1 + waste_percent/100, OpenStax, Elementary Algebra 2e, Solve Geometry Applications: Volume and Surface Area (rectangular area and proportional scaling), Sherwin-Williams Paint Calculator (product coverage is published per product and must be entered from the current data sheet), ISO 12944-5, Paints and varnishes - Corrosion protection of steel structures by protective paint systems: spreading rate from volume solids and dry film thickness and NIST Special Publication 811, Appendix B.9 (US gallon = 3.785 411 784 L exactly; international foot = 0.3048 m exactly).
Research R371-GT-1: 100 m2, two coats at 10 m2/L example
With Net paintable area: 100, Coats: 2, Coverage rate: 10, Waste allowance: 0, the calculator returns Paint needed: 20, Net paintable area: 100, Coverage rate used: 10. This example is checked against an independent source in the test suite.
What you can compare
Change one input at a time to see how it affects Paint needed, Net paintable area and Coverage rate used. The inputs you can vary are What to work out, Area unit, How the area is given, Net paintable area, Room length and Room width.
Results are general information, not financial, tax, legal, medical or engineering advice. Check any decision that matters with a qualified professional.
See something wrong? Report a problem with this calculator
Frequently asked questions
How do you calculate how much paint you need?
Works out how much paint a job needs from the net paintable area (or room dimensions), the number of coats, the product coverage rate and a waste allowance, then converts that into tins, litres. Open “How this is worked out” beside the result to see each step for your own figures.
How much paint is for 1 sq ft?
On the figures this page opens with — net paintable area 100, coverage rate 10 and waste allowance 0% — the paint needed is 20 L. No single number fits everyone: change any figure above and the answer updates as you type, with each step of the arithmetic beside it.
How many sq ft will 1 gallon of paint cover?
It needs What to work out, Area unit, How the area is given, Net paintable area, Room length and Room width. Nothing else is required, and the figures stay in your browser.
How much paint for a 10x10?
The result gives Paint needed, Net paintable area, Coverage rate used, Tins to buy, Area the paint on hand covers and Paint cost, each labelled with its unit so the figure can be read on its own.
What information do I need for the paint calculator?
You need What to work out, Area unit, How the area is given, Net paintable area, Room length, Room width, Wall height and Paint the ceiling too. The page opens with default figures that give paint needed of 20.00 L, so you can see the scale before entering your own.
What does this paint calculator show?
It shows Paint needed, Net paintable area, Coverage rate used, Tins to buy, Area the paint on hand covers, Paint cost, Labour cost and Total cost, with the working and any warnings for your entries.