Paint Calculator
Calculate how much paint you need for room walls and an optional ceiling, with product coverage, coats, openings, and can rounding shown separately.
- Net paintable area
- 436 ft²
- Coverage across 2 coats
- 872 ft²
- Paint before allowance
- 2.49 gal
- Paint with allowance
- 2.49 gal
- Purchased paint
- 3 gal
- Excess after whole cans
- 0.51 gal
Coverage varies by product, surface texture, porosity, color change, and application. Use the selected paint’s label value.
Show calculation
[2 × (12 + 10) ft × 8 ft − 36 ft² + 120 ft²] × 2 coats ÷ 350 ft²/gal × (1 + 0%) = 2.49 galTransparent method and editable product assumptions. Verify current labels and project requirements.
How this calculator works
The wall paint calculator finds room perimeter as 2 × (length + width), multiplies it by wall height, and subtracts the combined area of doors and windows that will not be painted. Optional ceiling area is then added.
Net paintable area is multiplied by the whole number of coats. The coat-weighted area is divided by the editable square-foot coverage per gallon. One optional allowance is applied before the exact gallons are divided by container size and rounded up.
Sherwin-Williams describes about 350–400 ft² per gallon as typical and notes that surface type, texture, condition, and application change product requirements. Use 350 as a conservative reference only when the selected paint does not provide a better label value. Separate colors, primers, trims, and products should be calculated separately.
Formula
Gallons = [(room perimeter × wall height − openings + ceiling area) × coats ÷ coverage] × (1 + allowance); cans = ceil(gallons ÷ can size)The live substitution appears with your result.Control example: 12 × 10 × 8 ft room
Four walls total 352 ft². Subtract 36 ft² of openings and add a 120 ft² ceiling for 436 ft² per coat.
Two coats create 872 ft² of coverage. At 350 ft² per gallon, the exact need is 2.49 gal, so buy three 1-gallon cans.
Assumptions and limits
- The room is rectangular and all four walls share one height.
- Opening area includes only surfaces not receiving this paint.
- Ceiling area uses the same product, coverage, coats, and color as the walls.
- Coverage comes from the selected paint for the actual surface condition.
Common measuring mistakes
- Using floor area as total wall area.
- Forgetting to multiply paintable area by the number of coats.
- Combining primer and finish paint in one coverage calculation.
- Rounding each wall to a full gallon instead of combining compatible areas first.
Sources
Product-specific values remain editable. These sources support the method and stated examples; they are not a universal substitute for your supplier’s current label.
- Sherwin-Williams Paint Calculator FAQ States that a gallon typically covers about 350–400 ft² and that application and surface conditions change requirements.
- Sherwin-Williams Painting FAQs Describes calculating surface area, dividing by product coverage, and treating theoretical coverage as product- and surface-dependent.
- Sherwin-Williams measuring guidance Supports multiplying each wall’s height by width, subtracting large openings, and checking the selected paint label.
Questions people ask
How much paint do I need for a room?
Calculate net wall and optional ceiling area, multiply by coats, divide by the selected paint coverage, and round the final order to whole containers.
How many square feet does a gallon of paint cover?
Sherwin-Williams gives about 350–400 ft² per gallon as typical. The actual product label and surface condition control the estimate.
Should I subtract windows and doors?
Subtract the combined area of openings that will not receive this paint. Do not subtract trim if it receives the same product.
Does the calculator include two coats?
Yes. The default is two, and the coat count is editable. Primer or a different finish should be calculated separately.
Why does the result round up to whole cans?
Paint is purchased in container increments. The page shows exact gallons and the excess created by your selected can size.