Primary material
3 1-gal cans
Interior paint gallons
Use the calculated gallon count as the starting point, then verify color, sheen, base, and label coverage before buying.
Paint calculator
Paint calculator for room gallons, coats, and primer.
Estimate interior wall paint from room dimensions, doors, windows, coats, ceiling choice, primer, and label coverage before building a shopping list.
Quick reference
Paint for common room sizes
Two coats on 8 ft walls with one door and two windows subtracted, at 350 sq ft per gallon with the default 10% extra.
| Room size | Wall area | Walls, 2 coats | Walls + ceiling |
|---|---|---|---|
| 10 x 10 ft | 270 sq ft | 2 gal | 3 gal |
| 12 x 12 ft | 334 sq ft | 3 gal | 4 gal |
| 12 x 15 ft | 382 sq ft | 3 gal | 4 gal |
| 15 x 20 ft | 510 sq ft | 4 gal | 6 gal |
| 20 x 20 ft | 590 sq ft | 4 gal | 7 gal |
Wall area is the room perimeter times the wall height, minus doors and windows.
Quick paint answers
Common room checks
12 x 12 bedroom, 2 coats
3 gal
334 sq ft paintable
2.10 gal calculated
10 x 12 office, 2 coats
2 gal
317 sq ft paintable
1.99 gal calculated
20 x 15 living room, 2 coats
4 gal
545 sq ft paintable
3.43 gal calculated
Shopping list
Compare paint, primer, and prep supplies
Optional primer
0 1-gal cans
Interior primer
Use primer for new drywall, stains, patched walls, strong color changes, or when the paint label recommends it.
Application kit
Roller, brush, tray, and tape
A basic room usually needs a roller frame, covers, angled brush, tray liners, painter tape, and drop cloths.
Prep and repair
Spackle, sanding sponge, and caulk
Patch nail holes, sand rough spots, and caulk trim gaps before you commit to final paint quantities.
Formula shown
How paint estimates work
Wall and opening area
wall area = 2 x (length + width) x height; openings = doors x 20 + windows x 15
Coats and coverage
paint gallons = paintable area x coats x allowance / sq ft per gallon
Buying round-up
1-gal cans = ceil(calculated gallons); quart equivalent = round up to the next 0.25 gal
Sources
- Lowe's Paint Calculator — paint and primer coverage ranges and room-area calculator structure
- Sherwin-Williams Paint Calculator — manufacturer room paint estimating workflow
- Benjamin Moore Paint Calculator — room dimensions, doors, windows, and paint quantity estimate context
- BEHR Premium Plus Interior Paint — retail 1-gallon interior paint product and coverage context
Sources checked
Checked against
Coverage rates checked against paint manufacturer and retailer calculator guidance.
How we check our numbersLast updated: June 21, 2026
Estimate only.
This calculator is not a quote. Verify product yield, price, delivery minimums, and local conditions with your supplier or contractor before buying materials.
Area audit
384 sq ft
Raw wall area before openings.
Openings removed
50 sq ft
Planning area for doors and windows.
Ceiling add-on
0 sq ft
Only included when the ceiling option is on.
Related paint tools
Need trim or exterior siding instead?
Trim and exterior siding use different formulas, so each has its own focused calculator.
FAQ
Paint calculator questions
Quick answers for room paint gallons, coats, primer, doors, windows, and coverage per gallon.
How much paint do I need for a room? + -
Measure the room length, width, and wall height. The calculator estimates wall area, subtracts doors and windows, multiplies by coats, then divides by paint coverage per gallon.
How much does one gallon of paint cover? + -
Many interior paints list about 350 to 400 square feet per gallon per coat, but texture, color change, application method, and product label coverage can change the real number.
Should I include doors and windows? + -
Yes when you want a tighter estimate. This calculator subtracts 20 square feet per door and 15 square feet per window as a planning shortcut.
Do I need primer? + -
Primer is common for new drywall, stains, patched walls, porous surfaces, glossy surfaces, and strong color changes. Turn on primer when the job needs a separate primer coat.
Why does the calculator round up gallons? + -
Paint is commonly bought by the gallon, and a little extra helps with touchups and roller loading. Always verify the final amount against the paint can label.