Coverage formula
Wall area for a rectangular room = 2 × (length + width) × height. Subtract doors (~20 sq ft) and windows (~15 sq ft each, adjustable). Gallons = paintable area × coats ÷ coverage. Default coverage is 350 sq ft/gallon per coat—porous or dramatic color changes may need more.
Worked example
A 14 × 12 × 8 ft room has wall area 2×(14+12)×8 = 416 sq ft. Minus 2 doors and 2 windows (40+30) → 346 sq ft paintable. Two coats at 350 sq ft/gal ≈ 1.98 gallons—buy 2 gallons plus a little for touch-ups, or 3 if changing from dark to light.
Ceilings and exteriors
This tool focuses on four walls. Add ceiling area (L×W) separately if you are painting it. Exterior siding with texture can cut effective coverage sharply—check the can.
Common mistakes
- Using only floor area instead of wall area.
- Forgetting closets and hall returns.
- Assuming one gallon always covers 400 sq ft on rough plaster.
| Room | Approx. wall area | Gallons (2 coats) |
|---|---|---|
| 10×10 | ~300 sq ft | ~1.7 gal |
| 12×12 | ~350 sq ft | ~2.0 gal |
| 12×16 | ~430 sq ft | ~2.5 gal |
Assumptions and limits
The paint calculator results are planning estimates for rectangular or cylindrical shapes with uniform depth. Real sites have slopes, voids, and product variation. Always confirm coverage with the manufacturer label and local building practices before you buy large quantities.
Unit toggles switch input labels between US imperial and metric. Shareable URLs store your inputs in the query string for convenience, while the canonical tag stays on the clean page URL so search engines do not index every parameter combination.
Shopping checklist
- Write down the calculator outputs (volume, bags, or piece counts) and round up for waste.
- Call your supplier for density, dye lot, or delivery minimums when ordering bulk material.
- Check access for trucks, wheelbarrows, and staging space before delivery day.
- Photograph existing conditions so you can revisit dimensions if a helper measures differently.
Buy all finish coats from the same batch when possible, and keep a labeled quart for touch-ups after furniture goes back in place.
FAQ
How much does a gallon of paint cover?
Many interior paints list about 250–400 sq ft per gallon per coat depending on surface and color change. This tool defaults to 350.
Related guides
Sources
- Sherwin-Williams – Coverage guidelines (typical) Used for: Typical interior coverage band; YardTally defaults to 350 sq ft/gal. Checked .
Estimates only—confirm bag yields on the product label and check local building codes before you pour or order. Not affiliated with QUIKRETE, Sakrete, Sonoco, or any manufacturer named in the sources. Found an error? Tell me.
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