What to buy
Gallons, quarts or a pail?
At typical prices, 2 gallons ($81) is the cheapest way to cover 1.99 gal. Quarts or a pail would not save you money.
The calculator tries every combination of 5 gallon pails, gallons and quarts that holds enough paint, and picks the cheapest. It uses your price where you entered one and the middle of the typical range where you did not. A tie goes to the mix with fewer cans.
- Quarts only help for the last part of a gallon: 4 quarts always cost more than the gallon, so a fourth quart is never used.
- A pail is only considered from 4 gallons up. At typical prices a 5 gallon pail ($137.50) beats 5 gallons ($202.50).
- Type the price on your store's shelf above and the mix updates. Sale paint can change the answer.
How it works
The formula
surface = wall (+ L × W for the ceiling)
gallons = surface × coats ÷ 350, then round up to what stores sell
Assumptions
- One gallon covers 350 sq ft per coat. Cans say 350 to 400 sq ft; we use the low end so you do not run short. Rough or dark walls use more.
- A standard door takes off 20 sq ft and a window 15 sq ft. Leave doors and windows at 0 to paint the full wall.
- Primer goes on in one coat at 250 sq ft per gallon, so it needs more gallons than one coat of paint.
- The ceiling is length × width and gets the same number of coats as the walls. Trim, baseboards and cabinets are not included.
- Metric: type meters. The room is converted to feet for the math, areas show in m² with sq ft beside them, and paint still comes in US gallons (3.8 L) and quarts (0.9 L).
Worked example
A 12 × 12 ft room, 8 ft walls, 1 door, 1 window, 2 coats
- Walls: 2 × (12 + 12) × 8 = 384 sq ft
- Take off the door and window: 384 − 20 − 15 = 349 sq ft
- Two coats: 349 × 2 = 698 sq ft of paint
- Gallons: 698 ÷ 350 = 1.99, so buy 2 × gallons
- At $40.50 a gallon (the middle of our typical range): $81
Common room sizes, 2 coats
| Room | Wall sq ft | Gallons needed | Buy |
|---|---|---|---|
| 10 × 10 ft | 285 | 1.63 | 2 × gallons |
| 12 × 12 ft | 349 | 1.99 | 2 × gallons |
| 12 × 14 ft | 381 | 2.18 | 2 × gallons + 1 × quart |
| 15 × 20 ft | 525 | 3.00 | 3 × gallons |
8 ft walls, 1 door and 1 window deducted, no ceiling, 350 sq ft per gallon. The Buy column is the cheapest mix at typical prices.
Questions people ask
How much paint do I need for a 12x12 room?
With 8 ft walls, 1 door, 1 window and 2 coats you need 1.99 gallons, so buy 2 × gallons. Add the ceiling and it rises to 3 gallons.
How many coats of paint do I need?
Two is the standard. One coat is fine over the same color in good shape. Use three for a big jump, such as dark red to white. For this room that is 1 gallon for 1 coat, 2 gallons for 2 coats, 3 gallons for 3 coats.
Does primer count as a coat?
No. Primer is a separate product and covers about 250 sq ft per gallon. Tick "Add primer" and it is added to the list as one coat: 2 gallons for this room. Many paint-and-primer-in-one cans still need two coats of color.
Is a 5 gallon pail cheaper than gallons?
Usually, from about 4 gallons up. At typical prices a pail costs $137.50 against $202.50 for 5 separate gallons. The list above checks this with your prices.
How much does a gallon of paint cover?
About 350 to 400 sq ft per coat; the can tells you. We use 350. At 400 your 698 sq ft room would need 2 gallons, so rounding up covers the difference.