How to calculate how much paint you need
The formula is: paintable area ÷ coverage per gallon × number of coats. One gallon of paint typically covers 350–400 square feet per coat. This calculator measures all four walls plus the ceiling, then subtracts space for doors and windows so you don't overbuy.
How many coats do you need?
For most repaints over a similar color: 1–2 coats. Going from dark to light, or painting new drywall: 2–3 coats. Using a primer first reduces the number of finish coats needed and improves color accuracy.
Paint coverage by finish
| Finish | Coverage per gallon | Best for |
|---|---|---|
| Flat / Matte | 350–400 sq ft | Ceilings, low-traffic walls |
| Eggshell | 350–400 sq ft | Living rooms, bedrooms |
| Satin | 300–350 sq ft | Kitchens, bathrooms |
| Semi-gloss | 300–350 sq ft | Trim, doors, cabinets |
| Gloss | 250–300 sq ft | Furniture, accent pieces |
Tips for less waste
Always buy a little more than the minimum — a quart (0.25 gal) extra is usually enough for touch-ups. Paint leftover in a sealed can keeps for 2–5 years if stored at room temperature. Label the can with the room and color code for easy future touch-ups.
How Much Paint for Common Scenarios
Not sure what numbers to plug in? These quick answers cover the most common painting questions.
How much paint for a 10×10 room?
A 10×10 room with 8-foot ceilings has roughly 320 sq ft of wall area before subtracting doors and windows. That's about one gallon per coat. For a standard two-coat job, plan on 2 gallons for walls — plus an extra quart if you're painting the ceiling. Enter your exact dimensions into the calculator above to get a precise number.
How much paint for a door?
A standard interior door face is about 20 sq ft (roughly 32 in × 80 in). One quart of paint covers a door front and back with two coats, with paint to spare. For an exterior door that takes more abuse, buy a full quart of exterior enamel per coat. Don't forget to count the door frame separately — add another half-quart for the trim.
How much paint for one wall?
A typical wall — 10 ft wide and 8 ft tall — is 80 sq ft. At 350–400 sq ft per gallon, a single quart handles one wall with one coat and most of a second coat. For a bold accent-wall color that needs two full coats, one quart is usually enough. If your wall is larger than 12 × 9 ft, step up to a half-gallon.
Methodology & sources
How this calculator works: it takes your total wall (and optional ceiling) area, subtracts doors and windows, then divides by the paint's coverage per gallon and multiplies by the number of coats. One gallon typically covers 350–400 sq ft per coat on primed, smooth surfaces; rough or porous surfaces cover less. Sources: the 350–400 sq ft/gallon figure follows published coverage rates from major paint makers (e.g., Sherwin-Williams, Behr). Estimates are for planning only. Last reviewed: by the Toolchive Team.