How much paint do you need for a job? Enter the paintable area, number of coats and coverage rate to calculate gallons (or litres), including waste, and see how much to buy.
Calculate paint needed
Calculated from your inputs. Buy quantity rounds up.
See how this was calculated
| Net paint | — |
| Waste allowance | — |
| Total needed | — |
| Buy (rounded up) | — |
Paint = (area × coats ÷ coverage) × (1 + waste%). Buy quantity always rounds up — an opened can keeps for touch-ups.
How to read your result
400 sq ft, 2 coats, coverage 350 sq ft/gal, 10% waste:
- Net: 400 × 2 ÷ 350 = 2.29 gal
- With waste: 2.29 × 1.10 = 2.51 gal
- Buy: 3 gallons (≈ 10 quarts)
These are example numbers to show the math. Enter your own job details above.
Which trades is this for?
For painting contractors estimating how many gallons a job needs.
- Interior painters: room-by-room estimates.
- Exterior painters: whole-house repaints.
- Drywall contractors: primer coverage on new work.
Assumptions & limits
- Coverage varies by surface and application. Rough, porous or previously unpainted surfaces absorb more paint. Dark-to-light colour changes may need more, and spraying uses more than rolling. Check the can and adjust your numbers.
- Use the actual paintable area. Subtract large windows, doors and anything you aren’t painting for a more accurate estimate.
- Purchase quantities round up. It’s better to have a leftover quart for touch-ups than run out halfway through a wall.
- Primer counts as a separate coat. Include it in the coats field if you’re priming.
Common questions
How much does a gallon of paint cover?
Most interior paints claim 350–400 sq ft per gallon per coat on a smooth, primed surface. Actual coverage is often 10–20% less on textured walls, bare drywall or major colour changes. Use the waste field to account for that.
Do I count primer as a coat?
Yes, if you’re buying primer separately. Enter the total number of coats, including primer. The calculator treats every coat the same, though primer coverage per gallon is often higher than paint. Run a separate calculation if you need a more precise estimate.
How many coats do I need?
Two finish coats over primer is standard for a durable finish. One coat can work for a same-colour refresh on a surface in good condition. Going from dark to light usually calls for a tinted primer plus two finish coats.
Guides by trade
Worked examples showing how painters use this calculator with their own numbers:
Related free tools
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