Free estimate — verify against local code before building
Paint Calculator
Gallons of paint and primer per room, plus tape, rollers, and cloths.
What this calculator includes
Enter room size, representative door and window deductions, surfaces, and coats to estimate whole gallons of paint and primer. Starting coverage values are editable because the selected product label, surface texture and porosity, preparation, and application method control actual yield. The input-specific breakdown keeps gross geometry, deductions, coating area, exact gallons, and whole-can rounding separate.
How to use this paint calculator
- 01
Measure the room
Measure length, width, and ceiling height in feet. For an L-shaped room, split it into rectangles and run each separately.
- 02
Count doors and windows
Starting deductions represent a 3 by 7 ft door and 3 by 5 ft window. Edit them to match the openings, and do not deduct surfaces that will also be painted.
- 03
Pick coats and primer
Choose coats and primer from the selected coating instructions and the prepared substrate. Hide, color change, porosity, repairs, and stains can change the system.
- 04
Buy by the gallon
Round up to whole gallons and have them all tinted at once — tint batches can vary slightly, and leftover paint handles touch-ups later.
Calculation sources and review
Primary references and formula assumptions are linked so you can verify them against the selected product, supplier, and adopted local requirements.
Internal formula review completed July 13, 2026. What this review covers
- Sherwin-Williams Paint Calculator FAQ (opens in a new tab)
Manufacturer planning range for paint and primer coverage and reminder that surface and application conditions change yield.
- BEHR Interior Paint Coverage Guidance (opens in a new tab)
Manufacturer coverage range and direction to use the selected product label.
- US EPA Lead Renovation, Repair and Painting Guidance (opens in a new tab)
Federal lead-safe requirements for covered renovation work in pre-1978 housing and child-occupied facilities.
Frequently asked questions
How much paint do I need for a 12×12 room?
Two gallons covers a 12×12 room with 8 ft ceilings for two coats on the walls. The math: 384 sq ft of gross wall minus one door (21 sq ft) and two windows (30 sq ft) leaves 333 sq ft; two coats is 666 sq ft, and at 350 sq ft per gallon that rounds up to 2 gallons.
How many square feet does a gallon of paint cover?
Manufacturer planning guidance commonly spans roughly 250 to 400 sq ft per gallon, but the selected product data and label govern. Texture, porosity, preparation, tools, and application losses can reduce actual coverage, so this calculator makes the value editable.
Do I need primer before painting?
Primer selection is product- and substrate-specific. Bare or patched material, stains, gloss, and large color changes often need a compatible primer or additional preparation; follow the coating manufacturer's system.
How much do I deduct for doors and windows?
The starting allowances are 21 sq ft for a representative 3 by 7 ft door and 15 sq ft for a representative 3 by 5 ft window. Edit the values or measure large and unusual openings directly.
Is one coat of paint ever enough?
Required coats depend on the selected coating, color, sheen, substrate, preparation, and application. Use the product instructions and a test area rather than assuming a universal one- or two-coat rule.