Details
Type feet and inches like 12'6" or just 12.5. Everything is saved on this device, so your list is still here in the shop.
About the paint calculator
Buying paint is a guessing game: buy too little and you make a second trip (and the new can may not match), buy too much and it sits in the garage for years. This calculator works it out from the size of your room.
Enter the length, width and height of the room, and how many doors and windows it has. The calculator finds the wall area, takes away the doors and windows, multiplies by the number of coats, and divides by how much one gallon (or litre) covers. You see the paint you need and the cans to buy — for example *2 × 1 gallon + 1 × 1 quart* — and the cost if you add a price.
Painting several rooms? Add each one. Painting just an accent wall? Choose One wall.
How to use it
- Choose Feet & inches or Metres & cm
- Type the length, width and height of the room (12'6" and 12.5 both work)
- Enter the number of doors and windows
- Pick the number of coats — two is normal
- Tick Paint the ceiling too if you are painting it with the same paint
- Read what you need, and press Copy the list to take it to the shop
How the paint is worked out
- Wall area = the distance around the room × the height. A 12 × 10 ft room with 8 ft walls has (12 + 10 + 12 + 10) × 8 = 352 sq ft of wall.
- Minus doors and windows — a standard door is about 21 sq ft (1.95 m²), a window about 15 sq ft (1.4 m²).
- × the number of coats.
- ÷ the coverage — how much one gallon or litre paints. Most interior paint covers 350–400 sq ft per gallon (about 9–10 m² per litre) in one coat on a smooth wall.
So the 12 × 10 ft room with one door and one window needs (352 − 36) × 2 ÷ 350 = 1.8 gallons for two coats: buy 2 gallons.
Paint for common room sizes
Two coats, 8 ft (2.4 m) walls, one door and one window, 350 sq ft per gallon:
| Room size | Wall area | Paint needed | Buy |
|---|---|---|---|
| 10 × 10 ft | 284 sq ft | 1.6 gallons (6.1 L) | 2 gallons |
| 10 × 12 ft | 316 sq ft | 1.8 gallons (6.8 L) | 2 gallons |
| 12 × 12 ft | 348 sq ft | 2.0 gallons (7.5 L) | 2 gallons |
| 12 × 14 ft | 380 sq ft | 2.2 gallons (8.2 L) | 2 gallons + 1 quart |
| 14 × 16 ft | 444 sq ft | 2.5 gallons (9.6 L) | 3 gallons |
| 15 × 20 ft | 524 sq ft | 3.0 gallons (11.3 L) | 3 gallons |
| 20 × 20 ft | 604 sq ft | 3.5 gallons (13.1 L) | 3 gallons + 2 quarts |
How far a gallon goes
The number on the can is for a smooth, sealed wall. Rough and thirsty surfaces take more:
| Surface | Coverage per gallon | Per litre |
|---|---|---|
| Smooth, already painted wall | 350–400 sq ft | 9–10 m² |
| New drywall (after primer) | 300–350 sq ft | 7–9 m² |
| Textured wall or ceiling | 250–300 sq ft | 6–7 m² |
| Brick, block or stucco | 150–200 sq ft | 4–5 m² |
Change Coverage in the calculator to match your wall — or to the number printed on your paint.
Tips that save money
- Two coats is normal. One coat is enough only when you repaint in the same colour.
- Big colour change? Dark over light, or light over a strong colour, often needs a primer first, or a third coat.
- Buy all the paint at once. Cans mixed on different days can be a little different in colour. If you need several cans, pour them together in a bucket ("boxing") so the colour is even.
- Keep a little extra for touch-ups later — a quart is plenty.
- Trim, doors and window frames are usually painted with a different (gloss) paint, so they are not in this total.
Frequently asked questions
How much paint do I need for a 12x12 room?
About 2 gallons (7.5 litres) for two coats on 8 ft walls with one door and one window. Add about 1 more gallon if you also paint the ceiling.
How many square feet does a gallon of paint cover?
Most interior paint covers 350 to 400 square feet per gallon in one coat on a smooth wall. Textured or new walls take more paint, so plan on 250–300 square feet there.
Do I take away the doors and windows?
Yes — the calculator does it for you. A door is about 21 sq ft and a window about 15 sq ft. In a small room it makes little difference; in a room with big windows or glass doors it can save a whole gallon.
How much paint do I need for a ceiling?
The ceiling area is simply length × width. A 12 × 12 ft ceiling is 144 sq ft, so two coats need about 0.8 gallons — one gallon. Tick Paint the ceiling too to add it.
Should I buy gallons or quarts?
A gallon is four quarts but usually costs about the same as two or three. Buy whole gallons for the main job, and quarts only for the last bit — the calculator suggests the mix. For big jobs, a 5-gallon bucket is the cheapest.
How much paint for one accent wall?
Choose One wall and type its width and height. A 12 ft wide, 8 ft high wall needs about half a gallon for two coats — a single gallon is plenty.
Good to know
- Your rooms and settings are saved in this browser, so the list is still there when you are in the shop
- The calculator gives the paint for the walls and ceiling — not for trim, doors or primer
- Nothing is sent anywhere: it works in your browser, even offline once the page has loaded
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- Tile & Flooring Calculator — tiles or boxes of flooring
- Concrete Calculator — bags for a slab or post holes
- Mulch, Soil & Gravel Calculator — for the garden
- Unit Converter — feet, metres, gallons and litres
