Paintable wall area = perimeter x ceiling height, minus doors and windows. Gallons needed = (area x number of coats) / coverage per gallon. One gallon typically covers 350 to 400 square feet per coat on smooth, previously painted surfaces, and noticeably less on textured, porous or unprimed substrates.
Paint is the cheap part of a paint job, prep is the expensive part, but you still need the gallons right. Enter room dimensions and coats to get paintable area, gallons and material cost.
| Input | Value |
|---|---|
| Room perimeter | 68 |
| Ceiling height | 9 |
| Doors | 2 |
| Windows | 3 |
| Coats | 2 |
| Coverage per gallon | 375 |
| Paint price | 48 |
| Ceiling area to paint | 0 |
| Result | Value |
|---|---|
| Paintable area | 525 sq ft |
| Gallons needed | 2.8 |
| Gallons to buy | 3 |
| Paint cost | $144.00 |
| Area per coat | 525 sq ft |
| Cost per sq ft (material) | $0.27 |
The 350 to 400 square feet per gallon on the can assumes a smooth, sealed, previously painted surface. Knockdown texture, bare drywall, raw wood, masonry and any dramatic colour change all consume more, sometimes far more.
New drywall, patched areas, stains and big colour shifts need primer, and it has its own coverage rate. Calculate it as an additional coat rather than assuming the finish paint will handle it.
Material is a small fraction of a paint bid. Masking, sanding, patching, caulking, cut-in time and cleanup are where painting jobs are won or lost, so estimate those hours explicitly rather than folding them into a square-foot rate.
Roughly 350 to 400 square feet per coat on a smooth, previously painted surface. Expect meaningfully less on textured, porous or unprimed surfaces, and check the manufacturer's stated spread rate for the specific product.
Two is standard for most repaints. One may suffice for a same-colour refresh in good condition, while a dramatic colour change, bare substrate or deep-tint base often needs primer plus two finish coats.
Yes, for material quantity, using roughly 21 square feet per door and 15 per standard window. For labor, cutting in around openings usually takes more time than painting open wall, so do not deduct labor the same way.
WinkScope's free paint coverage calculator computes paintable wall area (perimeter x ceiling height minus roughly 21 sq ft per door and 15 sq ft per window), then gallons needed as area multiplied by coats divided by coverage per gallon. One gallon typically covers 350 to 400 square feet per coat on smooth previously painted surfaces, and less on textured or unprimed substrates. Free, no signup.