Free tool
Paint Calculator
Enter the room and get how many gallons to buy — paintable square footage, coats, and cost, with doors and windows subtracted. Free, no signup for the estimate.
Paint needed
0 gal
- Wall area0 ft²
- Less doors & windows0 ft²
- Paintable area0 ft²
- Total with coats0 ft²
- Paint cost—
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Or download it now (PDF)How to estimate paint for a job
Under-buy and you’re making a paint-store run mid-job with a half-painted wall drying to a lap mark; over-buy and you’ve got cans of a custom color you’ll never use again. A good paint estimate is four quick numbers and one subtraction.
1. Measure the wall area
For a rectangular room, add the length and width, double it for all four walls, and multiply by ceiling height: 2 × (length + width) × height. That’s your gross wall area in square feet. For an L-shaped room, split it into rectangles and add them up.
2. Subtract doors and windows
You’re not painting the glass or the door slab, so take them out: about 21 sq ft per door and 15 sq ft per window. On a small room this can drop you a whole gallon. If you’d rather keep a cushion, leave them in and treat the extra as insurance.
3. Multiply by coats
Two finish coats is standard for an even result and true color. Multiply your paintable area by the number of coats before you convert to gallons — a two-coat job needs twice the paint of a one-coat touch-up. Estimate primer separately when the surface calls for it.
4. Convert to gallons
Divide the total coverage you need by a gallon’s coverage — about 350 sq ft on smooth, primed walls, less on fresh drywall or textured surfaces. Round up to whole gallons; you can’t buy two-thirds of a can, and a little left over is normal for touch-ups.
Measuring the job is step one. Turning it into a priced, professional quote is faster inside CrewRivet. See the concrete calculator, the job pricing calculator, or painting business software.
Paint calculator FAQ
- How much paint do I need for a room?
- Measure the wall area — for a rectangular room that is 2 × (length + width) × ceiling height. Subtract about 21 sq ft per door and 15 sq ft per window, multiply by the number of coats, then divide by the coverage of a gallon (about 350 sq ft). Round up to whole gallons. This calculator runs all of that live as you type.
- How many coats of paint should I plan for?
- Two finish coats is the standard for an even, durable result — especially over a color change or patched drywall. Primer is separate: bare drywall, stains, or a drastic color change usually need a coat of primer first, which you should estimate the same way.
- How much does a gallon of paint cover?
- Most interior wall paints cover about 350–400 sq ft per gallon on one coat over a smooth, primed surface. Rough or porous surfaces (fresh drywall, textured walls, bare wood) drink more and cover less, so estimate on the lower end when the surface is thirsty.
- Should I subtract doors and windows?
- For a tighter estimate, yes. A standard door is roughly 21 sq ft and an average window about 15 sq ft of surface you are not painting. On a small room it is the difference between buying two gallons and buying one — but if you are unsure, leaving them in just gives you a little extra.
- Is the calculator free?
- Yes — the live estimate is free with no email required. Enter your email only if you want the free Job Pricing Kit (pricing worksheet, markup cheat-sheet, and invoice + quote templates) sent to your inbox.