Paint Calculator
Estimate how much paint you need for walls, rooms, interior projects, renovations, repainting, and home improvement projects.
Room dimensions
Enter your room size, openings, coats, and paint coverage.
How to Use the Paint Calculator
Enter the length, width, and ceiling height of the room. The calculator estimates the wall area, subtracts standard door and window openings, multiplies by the number of coats, and divides the final area by your selected paint coverage rate.
Common Paint Coverage Rates
| Paint or Surface Type | Common Coverage |
|---|---|
| Interior wall paint | 300–400 sq ft per gallon |
| Primer | 200–300 sq ft per gallon |
| Textured walls | 200–300 sq ft per gallon |
| Fresh drywall | Usually needs primer plus paint |
| Strong color change | Often needs 2 coats or more |
Example Paint Estimate
For a 20 ft by 15 ft room with 8 ft walls, the wall area is about 560 square feet. After subtracting one standard door and two standard windows, the paintable area is about 509 square feet. With 2 coats, the total coat area is about 1,018 square feet. At 350 square feet per gallon, you would need about 3 gallons of paint.
Should You Add Extra Paint?
Yes. It is usually smart to round up to the next full gallon or litre. Extra paint helps with touch-ups, roller and brush waste, uneven coverage, surface texture, and small measurement differences. Keeping leftover paint is also useful for future repairs.
Frequently Asked Questions
How do I calculate how much paint I need?
Calculate wall area using room perimeter multiplied by wall height. Subtract doors and windows, multiply by the number of coats, then divide by the coverage rate.
How much does one gallon of paint cover?
Many interior paints cover about 300–400 square feet per gallon, but coverage depends on surface texture, paint type, primer, and application method.
Do I need two coats of paint?
Two coats are recommended for new walls, strong color changes, uneven surfaces, or better durability. One coat may be enough for touch-ups or similar colors.
Does this calculator include ceilings?
This version estimates wall paint only. Ceiling paint can be estimated separately by multiplying room length by room width and dividing by your paint coverage rate.