How much paint do I need?
Turn measured surface area into a practical purchase, with a worked room example.
Editorial review: October 11, 2026 · AI-assisted initial content · Editorial transparency
Divide the paintable surface area by the coverage printed on your paint can, then multiply by the number of coats. Add your chosen extra allowance, and round up to containers you can actually buy. Do this separately for every colour and sheen.
A complete room example
A room 12 ft long, 10 ft wide and 8 ft high has 352 sq ft of wall: 2 × (12 + 10) × 8. Subtract one 3 × 7 ft door and two 3 × 4 ft windows: 352 − 21 − 24 = 307 sq ft.
At 350 sq ft per US gallon and two coats, the theoretical requirement is 307 × 2 ÷ 350 = 1.7543 gallons. A 10% allowance brings that to 1.9297 gallons. Buy two 1-gallon cans for that paint group.
What if the ceiling is included?
The ceiling adds 12 × 10 = 120 sq ft. If it uses a different paint, calculate and round it separately. At the same settings it needs 0.7543 gallons including extra, so buy one gallon of ceiling paint. Adding the two theoretical volumes and rounding once can underestimate purchases when finishes differ.
Before you buy
- Use painted wall area, not floor area.
- Check whether the label’s coverage is per coat.
- Confirm container sizes and tint return policies with the retailer.
- Retain the colour code and product name for future touch-ups.
A metric example with two paint groups
For the 4 × 3 × 2.5 m room above, 35 m² of walls minus a 1.8 m² door and a 1.2 m² window leaves 32 m². With two coats at 10 m²/L and 10% extra, wall paint is 32 × 2 ÷ 10 × 1.1 = 7.04 L. A 12 m² ceiling at one coat and 12 m²/L needs 1.10 L including extra.
| Paint group | Needed | If only 2.5 / 10 L enabled |
|---|---|---|
| Wall product | 7.04 L | 3 × 2.5 L = 7.5 L |
| Ceiling product | 1.10 L | 1 × 2.5 L = 2.5 L |
If 1 L tins are also available, minimum-quantity purchasing becomes 7.5 L for the walls and 2 L for the ceiling. Enter the ceiling’s one coat and 12 m²/L as group overrides in the paint planner. Do not pool leftover amounts across different products.
Already know your area or paint quantity? Try the two-way paint coverage calculator.
Source notes
- Sherwin-Williams paint calculator — manufacturer planning guidance; check the specific product data sheet before buying.
- Benjamin Moore paint calculator — manufacturer estimating reference.
- Resene estimating worksheet — worked area and coverage methods.
Continue planning
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