Paint Calculator (Gallons & Cans per Room)
Wall area from room dimensions minus doors and windows, scaled by coats and coverage, then rounded into 1-gallon and 5-gallon cans with a cost estimate.
Paint — interactive calculator, computed instantly in your browser.
How Much Paint for a Room? Coverage, Coats, and Can Sizes
12 × 10 Room, 8 ft Walls: 512 ft² − Openings = 462 ft² → 2 Coats = 924 ft²
Paint is sold by coverage — square feet per gallon — so the whole job reduces to three numbers: wall area, coats, and can sizes. This calculator measures the room from length, width, and height, subtracts doors and windows, scales by coats and coverage, and rounds the answer into 1-gallon and 5-gallon cans with a cost estimate.
1. Wall Area From Room Dimensions
- 12 × 10 room at 8 ft: 2 × (12 + 10) × 8 = 352 ft² for four walls
- Accent wall? Add just that wall: length × height — the calculator accepts extra walls individually
- Cathedral ceilings and soffits add area fast — measure each plane separately and list it
- Wallpaper math uses the same area; rolls just replace gallons in the units column
2. Openings, Ceilings, and Texture
- Subtract openings: a standard door ≈ 20 ft², a window ≈ 15 ft² — paint does not stick to glass or trim
- Trim, baseboards, and doors themselves take a separate quart — do not fold them into wall gallons
- Textured walls (orange peel, knockdown) drink 10–20% more — bump the coverage field down to 300 ft²/gal
- Ceiling is a checkbox: length × width, usually flat white at its own coverage (ceilings spatter less than walls)
3. Coats and Coverage
- 350 ft²/gal is the standard rating — a same-color repaint can hit 400, a dark-over-light change drops below 300
- Two coats is the default for any color change; one coat only covers primed or matching surfaces
- Stain-blocking primer is its own gallon: markers, water damage, and knots bleed through paint without it
- Calculation example: 462 ft² net × 2 coats ÷ 350 = 2.64 gallons → 3 gallons
4. Cans, Rounding, and Cost
5-gallon buckets cost meaningfully less per gallon than singles — the calculator splits your number into an optimal mix of buckets and single cans so you neither undershoot nor store half-used surplus. Enter your price per gallon for the budget line. Buy all cans from one batch when possible: dye lots shift between runs, and a mid-wall color break shows forever in raking light.
🔗 Coverage Math Cross-References
Paint coverage is area per gallon — the same square-foot arithmetic anchors the 🔄 Conversion Hub measurement tools.
Measure the room once, buy the cans once: pair the area math below with concrete and flooring estimates for a full renovation budget.
Frequently Asked Questions (Paint)
For a standard 12 × 10 room with 8 ft walls: 352 ft² of wall area minus about 50 ft² of doors and windows = ~300 ft². At 350 ft² per gallon and two coats, that is 600 ÷ 350 = 1.7 gallons — so 2 gallons. The calculator runs your exact dimensions, openings, and coats.
Manufacturers rate most wall paints at 350 square feet per gallon on a smooth, primed surface. Real coverage drops with texture, porous drywall, and dark color changes — budget 300 ft² per gallon for repaints over strong colors, or plan on primer plus two finish coats.
Yes — paint does not cover glass or already-painted trim. A standard door is about 20 ft² and a window about 15 ft². The subtraction is small for typical rooms but adds up in window-heavy walls; the calculator takes door and window counts and deducts them automatically.
Only when repainting the same color over a sound surface. Any color change needs two coats for true color depth and even sheen — a single coat over a different shade looks patchy in daylight. Dark colors and stains need a primer coat first, which the calculator treats as an extra coat.