How to Calculate Paint Coverage
One gallon of paint covers approximately 350 square feet on smooth surfaces. The formula: wall area minus doors and windows, multiplied by number of coats, divided by 350.
Wall area = 2 × (length + width) × height. A standard door is about 21 square feet. A standard window is about 15 square feet.
How Many Coats Do You Need?
| Situation | Coats |
|---|---|
| Same color touch-up | 1 |
| Similar color over existing paint | 2 |
| Light over dark or dark over light | 2–3 (use primer first) |
| New drywall | 1 primer + 2 coats |
Tips to Buy the Right Amount
- Round up, not down— running out mid-wall means a visible color difference if the next batch doesn't match perfectly.
- Keep half a gallon extra — for future touch-ups. Store in a cool, dry place with the lid sealed tight.
- Textured walls need 15–20% more paint — this calculator assumes smooth surfaces.
FAQ
Does primer count as a coat?
No. Primer seals the surface but doesn't provide final color. Apply primer first, then your 1–2 coats of paint on top. Our calculator estimates paint only — budget for primer separately if needed.
How much does a gallon of paint cost?
Interior latex paint: $25–50 per gallon for mid-range brands. Premium paint (Benjamin Moore, Sherwin-Williams): $50–80 per gallon. Budget paint: $15–25 but often requires more coats.