Paint Calculator: How Much Paint Do I Need?
Enter your room size and the number of coats to see how many gallons of wall paint to buy, which cans make up that amount, and the cost.
Your estimate
Buy 2.5 gallons
2 × 1 gal + 2 × quart
- Wall area to paint
- 365 sq ft
- Openings subtracted
- − 51 sq ft1 door, 2 windows
- Paint needed
- 2.29 gal
- Coats
- 2
- Extra paint
- 10%
Add a price per gallon to see the cost.
How we got this: 365 sq ft × 2 coats ÷ 350 sq ft/gal × 1.10 = 2.29 gal, rounded up to whole cans: 2 × 1 gal + 2 × quart.
Buy all cans in one order and mix them in a bucket before you start. Tint can vary slightly between cans.
How the calculation works
- Wall area. The perimeter (2 × length + 2 × width) times the wall height, minus the doors and windows you enter (width × height × number).
- Paint. Wall area × coats ÷ the coverage on the can.
- Extra. We add 10% for cutting in, touch-ups and the paint left in the tray.
- Cans. We fill the amount with the fewest, largest cans, and use a quart (or small can) for the remainder when that wastes less.
Imperial example: a 12 × 14 ft room with 8 ft walls, one door and two windows has 365 sq ft of wall. Two coats at 350 sq ft per gallon plus 10% is 2.29 gallons: buy 2 gallons and 2 quarts.
Metric example: a 4 × 5 m room with 2.5 m walls, one door and one window has 41.7 m² of wall. Two coats at 8.6 m²/L plus 10% is 10.7 L: buy a 10 L tin and a 1 L tin.
Guides to save and share
Chart as a table: How much paint do I need for a room?
| Room | 1 coat | 2 coats |
|---|---|---|
| 10 × 10 ft (small bedroom) | 1 gal | 2 gal |
| 12 × 12 ft (bedroom) | 1.25 gal (1 × 1 gal + 1 × quart) | 2.25 gal (2 × 1 gal + 1 × quart) |
| 12 × 14 ft (main bedroom) | 1.25 gal (1 × 1 gal + 1 × quart) | 2.5 gal (2 × 1 gal + 2 × quart) |
| 14 × 16 ft (living room) | 1.5 gal (1 × 1 gal + 2 × quart) | 3 gal |
| 16 × 20 ft (large room) | 2 gal | 3.5 gal (3 × 1 gal + 2 × quart) |
How much extra paint should I buy?
| Walls | Extra paint | Why |
|---|---|---|
| Same color, smooth and primed | 5–10% | Touch-ups and paint left in the tray. |
| Color change or new drywall | 10–15% | Uneven absorption shows through the first coat. |
| Textured, brick or stucco | 15–20% | Rough surfaces hold more paint per square foot. |
Common mistakes
- Reading the coverage on the can as if it covers two coats. It is per coat.
- Forgetting that bare drywall, plaster and textured walls soak up more paint than painted walls.
- Buying cans on several trips. Tint can differ slightly between batches, so buy it all at once.
- Adding the ceiling to the wall area. Ceilings use a flat ceiling paint; work them out separately.
What else you'll need
- Primer for new drywall, patches, stains or a big color change.
- Painter's tape and drop cloths.
- Roller covers: 3/8 in (10 mm) nap for smooth walls, 1/2–3/4 in (12–20 mm) for textured walls.
- An angled 2–2 1/2 in brush for cutting in, plus a tray and liners.
- Spackle, sandpaper and caulk (sealant) for gaps around trim.
Frequently asked questions
How much does a gallon of paint cover?
Most interior wall paint covers 350–400 sq ft per gallon per coat on smooth, primed walls (about 8.5–10 m² per liter). Bare drywall, brick and textured walls take more. The can label gives the figure for that product.
How many coats of paint do I need?
Two coats for most walls. One coat can work when you repaint the same color over sound paint. New drywall or a big color change usually needs primer plus two coats.
Should I subtract doors and windows?
Yes. Enter each size with its trim: a standard interior door is about 3 × 7 ft (21 sq ft, 1.9 m²) and a typical window about 3 × 5 ft (15 sq ft). Add a row for each different size. The extra percentage covers cutting in around them.
How much paint do I need for a 12×12 room?
With 8 ft walls, one door and one window, the walls are about 348 sq ft. Two coats at 350 sq ft per gallon plus 10% is about 2.2 gallons: two gallons and one quart.
Do I need primer before painting?
Use primer on new drywall, patched areas, bare wood, stains, or when going from a dark color to a light one. Paint-and-primer products work over sound painted walls but do not replace primer on new drywall.
Is it cheaper to buy a 5-gallon bucket?
Usually, per gallon. The calculator picks a 5-gallon bucket when you would otherwise need four or more single gallons. Leftover paint keeps for years if the lid is sealed.
Related calculators
This is an estimate. Actual use depends on the material, the surface, the installation method, waste and site conditions. Check quantities with your supplier before you buy.