CalcCommons
Construction & Measurement

Paint Calculator

Estimate paint for walls or a measured area. Account for openings, coats, coverage, and whole containers before you buy.

01 · Set it up

Your inputs

Choose a quick value or enter your own. Example inputs are filled in to get you started.

Total door/window area to subtract; enter 0 if already excluded.
Use the product label. This is per coat, per US gallon.
02 · A little clarityEXAMPLE RESULT

Enter your measurements and calculate.

Calculated in your browser. Shared links include your entered values; only share information you intend to make public.

How to use

Choose room dimensions or enter an already measured area. Match the surface units, subtract only unpainted openings, then set coats and the coverage on your paint label. Choose the container size you will actually buy. Compare the exact requirement with the whole-container count.

For related tasks, try the Flooring Calculator.

Formula & how it works

Net area = wall perimeter × height + optional ceiling − openings. Paint gallons = net area × coats ÷ coverage × (1 + allowance/100). Containers = round up(paint volume ÷ container size).

Length12 ftWidth10 ftHeight8 ftNet surface312 ft²
Example inputs · Paintable surface · openings subtracted. Schematic, not to scale.

Worked examples

Example 1

A 12 × 10 ft room with 8 ft walls has 352 ft² of wall area. Subtract 40 ft² of openings: 312 ft². Two coats at 350 ft²/US gal with 10% extra require 1.9611 US gal, or two 1-gallon cans.

Example 2

For 500 ft² already measured net, enter known area 500 and openings 0. One coat at 400 ft²/US gal and no extra needs 1.25 US gal; buy two 1-gallon cans.

Assumptions & practical notes

The 350 ft²/US gallon default is an editable example, not a promise of coverage. Check the selected coating’s label; rough surfaces and dramatic color changes can need more.

Paint and primer are separate estimates. A US gallon is exactly 3.785411784 liters. Switching measurement units does not convert the numbers you have already entered.

Only one rectangular room is modeled. For multiple rooms, sum their net paintable areas and use known-area mode.

See our calculation methodology for unit definitions and testing practices.

Results are estimates for planning purposes. Verify measurements, product specifications, and applicable building codes before purchasing materials or starting work.

References & measurement guidance

Use the instructions for your selected product and the requirements that apply to your project. Example inputs are not universal specifications.

Frequently asked questions

Do I subtract doors and windows?

Enter the total unpainted opening area in the same square units as the surface. If your measured area already excludes openings, enter 0 to avoid subtracting twice.

Does two coats double the paint?

The estimate multiplies the net surface area by the coat count. Actual coverage can vary between coats; use the product’s instructions.

Can I buy paint in liters?

Yes. Choose liters for the container size. Coverage remains per US gallon and the calculator converts the required volume before rounding containers.

Does this include primer?

No. Run a separate estimate using the primer’s coverage and required coats.

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Calculate flooring boxes from room dimensions or a known area, with adjustable waste, package coverage, and optional material cost.

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