Paint Calculator
Enter your room dimensions below and get an instant estimate of how many gallons of paint you need for the walls. No guesswork, no leftover cans.
How to use this paint calculator
Measure your room's length, width and ceiling height in feet, count the doors and windows (they subtract from the paintable area), and pick how many coats you plan to apply. The calculator works out the total wall area and divides it by the standard coverage of one gallon (350 sq ft per coat). The result is rounded up to the nearest half-gallon so you always buy slightly more than you need - painting is far cheaper than a second trip to the store.
Tip: if you are also painting the ceiling, add about 25-30% more paint or use the same dimensions with the ceiling area added. Textured walls (knockdown, orange peel) absorb 10-20% more paint than smooth drywall.
Paint calculator FAQ
How do I calculate the wall area of a room?
Multiply the perimeter of the room (length + width, doubled) by the ceiling height: 2 x (L + W) x H. Subtract 15 sq ft for each window and 21 sq ft for each standard door.
Is 2 coats of paint always necessary?
Two coats give a more durable, even finish and better color depth. One coat is usually enough only for touch-ups or when repainting with the exact same color.
Can I use this calculator for exterior painting?
Yes - use the same formula but remember exterior paint covers slightly less (about 300-320 sq ft per gallon) because of the rough surface of siding and stucco.