Paint Calculator
Estimate how much paint you need for the walls of a room. Enter the room dimensions, openings, coats, and paint coverage to get a practical purchasing estimate.
Room Details
Room dimensions
Doors & windows
Average sizesPaint settings
Your paint estimate will appear here
Enter your room measurements above and select Calculate Paint.
How Much Paint Do You Need?
Paint requirements depend on more than the floor size of a room. Wall height, room perimeter, doors, windows, the number of coats, surface condition, and the coverage rate of the selected paint can all affect the final amount.
This calculator estimates wall paint by calculating the total wall surface, subtracting estimated door and window openings, applying the selected number of coats, and then adding your chosen waste allowance.
How the Paint Calculation Works
2 × (Length + Width) × Height
Wall Area − Door Area − Window Area
Paintable Area × Number of Coats
Coat Area × (1 + Waste %)
Adjusted Area ÷ Coverage Rate
Example Paint Estimate
Consider a room that is 15 feet long, 12 feet wide, and 8 feet high. With one average door, two average windows, two coats of paint, a coverage rate of 350 square feet per gallon, and a 10% allowance, the calculator first determines the total wall surface before deducting the estimated openings.
It then multiplies the paintable area by two coats and applies the selected waste allowance before dividing the total by the paint coverage rate.
Use the label on your paint
Coverage varies between products. When possible, replace the calculator’s default coverage rate with the value stated by the paint manufacturer.
Typical Paint Coverage
| Surface | Typical Coverage | What May Affect It |
|---|---|---|
| Smooth painted wall | 350–400 sq ft / gallon | Color change and paint formulation |
| New drywall | About 300–350 sq ft / gallon | Porosity and whether primer is used |
| Textured surface | Often below smooth-wall coverage | Texture depth and application method |
| Previously unpainted porous surface | May require substantially more material | Absorption and primer requirements |
Factors That Can Change Your Paint Estimate
Rough and textured walls generally use more paint than smooth surfaces.
Changing from a very dark color to a light color, or the reverse, may require additional coats.
New drywall, repaired surfaces, or dramatic color changes may require primer before painting.
Brushes, rollers, and spraying techniques can produce different real-world coverage rates.
Paint Calculator Questions
Does the calculator include the ceiling?
No. The current calculation estimates paint for the room’s walls only. Ceiling area is calculated differently and can be estimated by multiplying room length by room width.
Are doors and windows automatically deducted?
Yes. The calculator subtracts an estimated area for each door and window entered. These are average assumptions rather than measurements of your exact openings.
How many coats should I use?
Two coats are common for many interior projects, but the correct number depends on the existing wall color, surface, primer, paint product, and desired finish.
Why should I include a waste allowance?
A modest allowance can help account for application losses, surface variation, small measurement differences, and paint reserved for future touch-ups.
Is this paint estimate exact?
No. The result is a planning estimate. Actual paint usage can differ because of product coverage, wall condition, texture, application method, primer, and the dimensions of real doors and windows.