Paint Calculator
Estimate paint quantity and cost from a known surface area, coats and product coverage.
Project details
Enter your measurements below.
How much paint do you need?
Use this paint calculator when you already know the surface area you plan to paint. It converts area, number of coats, product coverage and a waste allowance into a practical purchase quantity, then rounds up to whole paint containers so you do not plan around a fraction of a gallon or litre.
Walls, ceilings, exterior surfaces and other projects where the paintable area is already known.
Recommended whole gallons or litres, plus the calculated paint need before rounding.
Coverage is the value you enter from the paint label or manufacturer specification.
How to use the Paint Calculator
- Enter the total paintable surface area. Deduct areas you are not painting before entering the number.
- Choose the number of coats. Two coats are common for many repainting jobs, but your product and surface may require a different number.
- Enter the stated coverage per gallon or litre from the product you plan to use.
- Set a waste allowance for roller/brush loss, touch-ups and small measurement differences.
- Enter the container price if you want an estimated paint-material cost.
Formula used by DIYGauge
What this result helps you decide
Use the recommended gallons or litres as a shopping estimate and compare it with the container sizes sold by your supplier.
Worked example: 500 sq ft, two coats
- Surface area
- 500 sq ft
- Coats
- 2
- Coverage
- 350 sq ft/gal
- Waste
- 10%
- Price
- $42/gal
The calculation is about 3.14 gallons, so DIYGauge recommends buying 4 gallons. At $42 per gallon, the estimated paint cost is $168.
Practical planning tips
Use the coverage printed for the exact product and surface type; primer, textured walls and porous surfaces can behave differently.
If you are changing from a very dark color to a very light color, plan coats based on the paint system you will actually use.
Keep some leftover paint from the same batch for future touch-ups when practical.
Common mistakes to avoid
Coverage printed on the can can change on porous, textured or previously unsealed surfaces.
Do not count primer as a finish coat unless that is how your product system is specified.
Paint Calculator FAQs
Does the calculator include primer?+
No. This tool estimates finish paint. Use the Primer Calculator separately when the project needs a primer coat.
Should doors and windows be deducted?+
Yes, if the area you enter includes them and they will not be painted. If you need automatic door and window deductions, use the Interior Paint Calculator.
Why does DIYGauge round up?+
Paint is normally purchased in fixed container sizes. Rounding up avoids returning a purchase quantity that cannot be bought as entered.
Is 10% waste always required?+
No. Waste is adjustable. Use a value that matches the project, surface, application method and how precise your measurements are.
How Much Paint Do I Need?
A practical method for turning wall area, coats and paint coverage into a realistic purchase quantity.