Paint Calculator
Work out how many gallons of paint a room or wall needs.
What you'll need to order
- interior wall paint
- ceiling paint
- primer
- painter's tape
- rollers and brushes
Prices vary by region and haul distance. Get quotes from at least two local suppliers.
How this calculator works
gallons = wall area ÷ 350 × number of coats
A gallon covers roughly 350 sq ft per coat on smooth, previously painted drywall. Textured, porous or new surfaces drop that to 250 or 300, and dark-over-light colour changes need primer regardless of coat count.
Worked example
With room length 14 ft, room width 12 ft, ceiling height 8 ft, number of coats 2 , this calculator returns 2.15 gal.
Paint needed by room size
Figures below assume room width 12 ft × ceiling height 8 ft × number of coats 2 . Change any measurement in the calculator to get your own numbers.
| Room length | Wall paint needed (gal) | Wall area (sq ft) |
|---|---|---|
| 8 ft | 1.60 | 280.0 |
| 10 ft | 1.78 | 312.0 |
| 12 ft | 1.97 | 344.0 |
| 14 ft | 2.15 | 376.0 |
| 16 ft | 2.33 | 408.0 |
| 20 ft | 2.70 | 472.0 |
Rooms 12 ft wide with 8 ft ceilings, two coats, with 40 sq ft deducted for a door and a window.
How much paint for a bedroom, bathroom or whole house?
| Job | Size | Wall paint needed | Material cost |
|---|---|---|---|
| Small bathroom | 8 ft × 6 ft × 8 ft × 2 | 1.05 gal | $26 – $79 |
| Bedroom | 12 ft × 11 ft × 8 ft × 2 | 1.87 gal | $47 – $141 |
| Living room | 18 ft × 14 ft × 9 ft × 2 | 3.06 gal | $77 – $230 |
| Open-plan kitchen and diner | 24 ft × 16 ft × 9 ft × 2 | 3.89 gal | $97 – $291 |
| Stairwell with high ceiling | 10 ft × 8 ft × 16 ft × 2 | 3.06 gal | $77 – $230 |
Figures are for walls only. Ceilings are shown separately in the calculator — a ceiling takes roughly a third of what the walls do.
Cost range uses $25–$75 per gallon for material only.
What does interior paint cost?
Material typically runs $25 to $75 per gallon. Paint only. A professional interior repaint typically runs $2 to $6 per square foot of floor area, including prep and two coats.
What moves the price:
- Quality tier — contractor-grade versus premium differs mainly in coverage and washability
- Sheen: flat is cheapest, high-gloss and enamel cost more
- Deep or saturated colours need a tinted primer and often a third coat
- Primer, which most jobs over bare or patched drywall need as a separate product
Prices are US averages and move with fuel, season and haul distance. Always get two local quotes before budgeting.
Paint coverage by surface
| Type | Coverage (sq ft per gallon) | Notes |
|---|---|---|
| Smooth primed drywall | 400.0 | Best case; the figure on the tin |
| Previously painted wall | 350.0 | What this calculator assumes |
| Light texture (orange peel) | 300.0 | Texture adds surface area |
| Heavy texture (knockdown) | 250.0 | Spraying is far more efficient here |
| Bare drywall, no primer | 200.0 | Prime instead — it costs less than the extra paint |
| Rough masonry or block | 175.0 | Block filler first on porous surfaces |
Tin coverage figures assume ideal conditions. The 350 sq ft used here is the realistic working figure for a repaint.
Paint quantity questions
How much does a gallon of paint cover?
About 350 sq ft in one coat on smooth, previously painted drywall. New drywall, textured walls and masonry soak up far more — expect 250 sq ft or less.
How many gallons do I need for a 12x14 room?
Just over two gallons for two coats on the walls, plus one gallon for the ceiling. Buy the extra quart rather than running out — matching a second batch of tinted paint is never exact.
Do I need primer?
Yes on bare drywall, over stains, and whenever you are covering a dark colour with a lighter one. Over an existing paint film in a similar shade, two coats of a quality paint will do without it.
How much paint do I need for a 12x12 room?
About 1.5 gallons for two coats on the walls, assuming an 8 ft ceiling. Add roughly half a gallon if you are painting the ceiling as well.
How much paint for a whole house interior?
A 2,000 sq ft home typically takes 12 to 16 gallons for walls and 4 to 6 for ceilings, at two coats. Trim and doors need another 2 to 3 gallons of enamel.
How much paint do I need for trim and doors?
A gallon of enamel covers about 6 average doors, or roughly 350 linear feet of baseboard. Most whole-house repaints need 2 to 3 gallons of trim paint.
Should I subtract windows and doors?
This calculator already deducts 40 square feet, about one door and one average window. If your room has a wall of glass or several large windows, subtract the extra area yourself.
Is one coat of paint ever enough?
Only when repainting the same colour on a sound surface, or with a paint-and-primer product over a very close shade. Every other case shows lap marks and uneven sheen after a single coat.