Free paint calculator
Paint Calculator
Calculate how much paint you need for walls and ceilings. Use room dimensions or a known gross wall area, subtract openings, set your own coats and product coverage, and add primer without automatically adding a waste factor.
Estimate paint and primer gallons
Coverage defaults are starting values only. Use the coverage listed for the actual paint or primer you plan to use.
1. Choose how to measure
Use room dimensions for a simple rectangular room, or enter a known gross wall area before deductions.
Enter wall area before doors, windows, and other exclusions.
2. Walls & openings
Subtract openings or non-painted wall areas from the gross wall area. Door and window area assumptions are editable.
Editable starting value. Replace it with your measured opening area when available.
Editable starting value. Replace it with your measured opening area when available.
Examples: cabinets, tile, wainscoting, or large openings.
3. Wall paint settings
Set the coat count and the coverage for the wall paint you actually plan to use.
Starting value only. Use the coverage listed for your paint.
Default 0%. No hidden waste factor is added.
4. Ceiling & primer
Ceiling paint and primer are optional and use their own coat counts and coverage.
Use the product's listed coverage.
Walls + ceiling is available when ceiling paint is included.
Use the primer's listed coverage.
5. Paint needed
Exact gallons are calculated from the inputs above. Whole-gallon equivalents are shown as a simple reference, not a guaranteed purchase recommendation.
Your measurements and coating settings are processed in your browser and aren't sent to us.
Material estimate only. Actual coverage can vary with the product, surface texture and condition, color change, application method, absorption, and jobsite conditions. Check the product label or technical data before finalizing material quantities.
How much paint do I need?
- Choose Room dimensions for a simple rectangular room, or Known gross wall area when you already have wall square footage before deductions.
- Subtract doors, windows, and any other wall areas that will not be painted.
- Set wall coats and paint coverage per gallon using the product information for the paint you plan to use.
- Add ceiling paint and primer only when they belong to the project.
- Review exact gallons and the whole-gallon equivalent for each coating separately.
Paint calculator formulas
2 × (length + width) × wall heightgross wall area − doors − windows − other exclusionspaintable area × coats ÷ coverage × (1 + extra %)round exact gallons up to the next whole gallonCoverage per gallon is editable because different paints, primers, surfaces, and application conditions can produce different real-world coverage. The calculator does not treat the default 350 sq ft/gal value as a universal rule.
Paint calculator FAQ
How many square feet does a gallon of paint cover?
Coverage varies by product and conditions, so this calculator lets you enter the coverage listed for the paint you plan to use. The 350 sq ft/gal starting value is editable and is not treated as a guarantee.
Should I subtract doors and windows?
If those openings will not receive the wall paint, subtract them from the gross wall area. The area per door and window is editable so you are not locked into a fixed assumption.
What does Known gross wall area mean?
It means wall area before doors, windows, and other exclusions are removed. Do not enter a net paintable area in that field and then subtract the same openings again.
Can I enter ceiling area directly?
Yes, in Known gross wall area mode. Turn on Include ceiling paint and enter the ceiling square footage. In Room dimensions mode, ceiling area is calculated from room length × room width.
How many coats should I enter?
Enter the number of coats planned for the job. The correct count depends on the project, product, existing surface, color change, and finish requirements.
How does primer affect the estimate?
Choose No primer, Walls, or Walls + ceiling. Primer uses its own coat count and coverage value, so it is calculated separately from finish paint.
Why can actual paint coverage vary?
Surface texture, porosity, condition, application method, product formulation, and jobsite conditions can change actual coverage. Use this as a planning estimate and verify the product information.