How much paint do I need?
Measure the length and width of the room and the height of the walls. Count the doors and windows: the calculator takes off 21 sq ft for each door and 15 sq ft for each window, the allowances Sherwin-Williams uses. If you're painting one feature wall, choose "One wall".
The answer starts with Sherwin-Williams' own example room, so you can check it against their worksheet. Benjamin Moore recommends two coats for full color development; previously painted walls can sometimes take one.
Source Sherwin-Williams · Painter Skills Program, Part 1: paint coverage worksheet (slides 32 – 37) ↗Benjamin Moore · Regal Select Matte (N548) technical data sheet: spread rate, coats, dry time, weight ↗
How to calculate paint
Here it is with your numbers:
- Add up the four walls and multiply by the height: (16 + 12 + 16 + 12) × 8 = 448 sq ft.
- Take off 21 sq ft for each door and 15 for each window: 448 − (2 × 21) − (3 × 15) = 361 sq ft.
- Multiply by the coats and divide by the coverage: 361 × 2 ÷ 350 = 2.0629 gallons, rounded to 2.06.
- Round up to whole cans: 3 gallons, or 2 gallons and 1 quart (a quart is a quarter of a gallon).
It means buying 3 gallons of paint, or 2 gallons and 1 quart, for 2 coats.
Paint is sold by the gallon and the quart (a quarter of a gallon), so always round up. Buying a quart on top of whole gallons often saves buying a whole extra gallon.
Source NIST Handbook 44 (2026) · Appendix C, General Tables of Units of Measurement (4 quarts = 1 gallon) ↗
How much does a gallon of paint cover?
What the paint makers say one gallon covers with one coat. Rough, porous or bare surfaces take more paint, so use the figure on your can, and the lower number if it gives a range.
| Source | Sq ft per gallon |
|---|---|
| Sherwin-Williams estimating worksheet | 350 |
| Benjamin Moore Regal Select Matte | 400 – 450 |
| Behr Ultra and Premium Plus (interior) | 250 – 400 |
Source Behr · Determine how much interior paint to buy (coverage per coat) ↗
Paint for common room sizes
Walls only, 8 ft high, with 1 door and 2 windows, two coats at 350 sq ft per gallon.
| Room | Area to paint | Buy |
|---|---|---|
| 10 × 10 ft | 269 sq ft | 2 gal |
| 12 × 10 ft | 301 sq ft | 2 gal |
| 12 × 12 ft | 333 sq ft | 2 gal |
| 14 × 12 ft | 365 sq ft | 3 gal |
| 16 × 12 ft | 397 sq ft | 3 gal |
| 16 × 14 ft | 429 sq ft | 3 gal |
| 20 × 16 ft | 525 sq ft | 3 gal |
FAQs
How much paint do I need?
Add up the length of the walls, multiply by the height, take off the doors and windows, then multiply by the coats and divide by the coverage per gallon. Sherwin-Williams' example room (16 × 12 ft, 8 ft walls, 2 doors, 3 windows) has 361 sq ft to paint: 1.03 gallons for one coat, so 2.06 gallons for two coats.
Source Sherwin-Williams · Painter Skills Program, Part 1: paint coverage worksheet (slides 32 – 37) ↗
How many square feet does a gallon of paint cover?
It depends on the paint and the wall. Benjamin Moore's Regal Select Matte data sheet gives 400 – 450 sq ft per gallon, "depending on surface texture and porosity". Sherwin-Williams' worksheet uses 350 sq ft per gallon. Use the figure on your can, and the lower number if it gives a range.
How much does a quart of paint cover?
A quart is a quarter of a gallon, so it covers a quarter as much: 87.5 sq ft at 350 sq ft per gallon, or 100 – 112.5 sq ft at Benjamin Moore's 400 – 450.
Source NIST Handbook 44 (2026) · Appendix C, General Tables of Units of Measurement (4 quarts = 1 gallon) ↗
How many gallons of paint do I need for a bedroom?
A 12 × 10 ft bedroom with 8 ft walls, 1 door and 2 windows has 301 sq ft of wall. Two coats at 350 sq ft per gallon take 1.72 gallons, so buy 2 gallons. Painting the ceiling as well adds 120 sq ft for each coat.
Source Sherwin-Williams · Painter Skills Program, Part 1: paint coverage worksheet (slides 32 – 37) ↗
How much does a gallon of paint weigh?
Benjamin Moore lists its Regal Select Matte at 11.5 lb per gallon, so 5 gallons of it weigh about 57.5 lb, plus the pail. Other paints differ a little: the weight is on each product's data sheet.
How long does paint take to dry?
For Benjamin Moore Regal Select at 77 °F and 50% humidity, it is dry to the touch in 1 hour and ready for a second coat in 1 – 2 hours. High humidity and cool temperatures make it take longer, and painted walls can be washed after two weeks.
How many square feet does 5 gallons of paint cover?
At Sherwin-Williams' 350 sq ft per gallon, 5 gallons cover 1,750 sq ft with one coat, or 875 sq ft with two.
Source Sherwin-Williams · Painter Skills Program, Part 1: paint coverage worksheet (slides 32 – 37) ↗
Sources
- Sherwin-Williams: Painter Skills Program, Part 1: paint coverage worksheet (slides 32 – 37)
- Benjamin Moore: Regal Select Matte (N548) technical data sheet: spread rate, coats, dry time, weight
- Behr: Determine how much interior paint to buy (coverage per coat)
- NIST Handbook 44 (2026): Appendix C, General Tables of Units of Measurement (4 quarts = 1 gallon)