Paint Calculator
Estimate paint for rooms, walls, ceilings, doors, windows, coats, primer, waste allowance, and project cost before you buy.
Paint room calculator
Estimate wall and ceiling paint by room size, coats, coverage, doors, windows, primer, waste, and project cost.
Room size and paint assumptions
Adds length × width to the paintable area.
Primer is estimated separately from paint coats.
Results
| Wall square footage | 0 |
| Ceiling square footage | 0 |
| Door/window deduction | 0 |
| Paintable square footage | 0 |
| Total coated square footage | 0 |
| Gallons before waste | 0 |
| Gallons with waste | 0 |
| Recommended gallons to buy | 0 |
| Estimated paint cost | $0 |
| Primer gallons | 0 |
| Primer cost | $0 |
Cost estimator
Edit the paint cost per gallon, coverage rate, primer cost, and primer coverage to match the product you plan to buy. The calculator rounds up to whole gallons because paint is normally purchased by the can.
Waste and extra paint
Default 10%. Add extra paint if your walls are textured, patched, dark-colored, unprimed, or if you want leftovers for touch-ups later.
Common paint assumptions
| Item | Default assumption |
|---|---|
| Door deduction | 20 sq ft |
| Window deduction | 15 sq ft |
| Paint coverage | 300–400 sq ft/gallon |
| Typical coats | 2 coats |
| Waste/extra | 10% |
Plain-English guide
The calculator starts with wall area: two times the room length plus width, multiplied by wall height. It subtracts standard door and window areas, optionally adds the ceiling, multiplies by the number of coats, then divides by paint coverage. Primer is estimated separately because primer coverage and cost can differ from wall paint.
Paint calculator FAQ
How many coats of paint do I need?
Two coats is a common default for interior walls. One coat may work for similar colors in good condition, while dark color changes, patched walls, or uneven surfaces may need primer and two finish coats.
Does primer count as a coat?
Primer is usually counted separately from paint coats. It helps seal surfaces, improve adhesion, and cover stains or strong color changes before finish paint.
How much paint do I need for one room?
Measure the room length, width, and wall height, subtract doors and windows, then multiply by coats. This calculator does that math and rounds the gallons up for buying paint.
Should I subtract windows and doors?
Yes, for a closer estimate. This calculator subtracts 20 square feet per door and 15 square feet per window by default.
How much extra paint should I buy?
A 10% extra allowance is a practical starting point. Buy more if walls are textured, patched, dark, unprimed, or if you want touch-up paint later.
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