Paint Calculator
Work out gallons of paint for a room from wall dimensions, doors, windows, and coats — with a buy-this-many answer.
Processed locally in your browser — nothing is uploaded.
Paint Calculator
Walls
Deducted at 21 sq ft each
Deducted at 15 sq ft each
Typical paint covers ~350 sq ft per gallon per coat
Results
- Wall area
- 352 sq ft
- Paintable area
- 301 sq ft
- Area to cover (all coats)
- 602 sq ft
- Paint needed
- 1.72 gal
- Buy
- 2 gal
After door and window deductions
Or 7 quarts for small jobs
Estimate assumes smooth, primed walls. Porous or dark surfaces may need more paint.
About Paint Calculator
Add each wall as length × height, tell it how many doors and windows to subtract, and pick your coat count. The calculator totals the paintable area, divides by the coverage rate, and rounds up to whole gallons (or quarts for touch-up jobs).
Doors are deducted at 21 sq ft and windows at 15 sq ft — the standard estimating shortcuts — and coverage defaults to 350 sq ft per gallon, the figure most paint brands print on the can.
Common uses
- Buy the right number of gallons for a bedroom repaint in one trip
- Compare paint needed for one coat vs two
- Estimate paint for a whole floor by adding every wall
Example
Input
Two 12×8 ft + two 10×8 ft walls, 1 door, 2 windows, 2 coats
Output
301 sq ft paintable → 1.72 gal exact → buy 2 gallons
Limitations
- Assumes smooth, primed surfaces; textured, porous, or dark walls need extra paint
- Door/window deductions use flat 21 and 15 sq ft estimating figures
- Ceilings and trim are not included — run them as separate calculations
Frequently asked questions
How much paint do I need for a 12x12 room?
A 12×12 room with 8 ft ceilings has about 384 sq ft of wall. Subtracting one door (21 sq ft) and one window (15 sq ft) leaves 348 sq ft, and two coats means covering 696 sq ft — just under 2 gallons at 350 sq ft per gallon.
How many square feet does a gallon of paint cover?
About 350 sq ft per coat is the figure most brands print on the can, and it's this calculator's default. Real coverage runs roughly 250–400 sq ft depending on the paint, the surface texture, and how porous or dark the wall is.
Does a second coat double the amount of paint I need?
For planning purposes, yes — this calculator multiplies the paintable area by the coat count, so two coats need twice the paint of one. In practice a second coat over a sealed first coat sometimes goes a little further, but buying for the full amount avoids a mid-job store run.
Should I subtract doors and windows from the wall area?
Yes — they can be a meaningful share of a small room's wall area. This calculator deducts a flat 21 sq ft per door and 15 sq ft per window, the standard estimating shortcuts, rather than asking you to measure each opening.
Are my room measurements sent to a server?
No. Every calculation runs in JavaScript in your browser — wall dimensions, door and window counts, and results are never transmitted or stored anywhere.