How it works
The calculator adds up the area of every ceiling, multiplies by the number of coats and divides by the coverage of your paint.
Ceiling area = Σ (Length × Width)
Paint = Ceiling area × Coats ÷ Coverage × (1 + Extra ÷ 100)
Cans = ⌈ Paint ÷ Can size ⌉
⌈ ⌉ means rounding up to the next whole number: you can’t buy part of a can. Rooms are added together before rounding, so you buy cans for the whole job, not per room.
The product list uses each manufacturer’s published spread rate – the low end where the data sheet gives a range – and the coverage used is shown with the result.
Measurements, coverage and can size are converted to one internal unit before calculating, so you can enter the ceilings in feet and inches and pick gallons or quarts for the cans. One US gallon equals four quarts.
Worked example
Inputs
- Ceilings 1
- Ceiling length 14 ft, Ceiling width 12 ft
- Ceilings 2
- Ceiling length 10 ft, Ceiling width 10 ft
- Number of coats
- 2
- Paint product
- Your own coverage
- Coverage
- 350 sq ft/gal
- Extra paint
- 0 %
- Can size
- 1 gal
Result
- Ceiling area
- 268 sq ft
- Coverage used
- 350 sq ft/gal
- Paint needed
- 1.53 gal (6.13 qt)
- Cans
- 2
Common mistakes
- Using another paint’s coverage. Ceiling paints differ – pick your product or type the figure from your can – and textured or popcorn ceilings take much more paint than the data sheet says.
- Measuring a sloped or vaulted ceiling as if it were flat. The sloped surface is larger than the floor below it.
- Forgetting closets and hallways that share the same ceiling color – add them as extra rows.
- Planning one coat over a stained or dark ceiling. Stains may need a primer first, which has its own coverage.
Assumptions and limits
- Each ceiling is a flat rectangle with the length and width you enter. For L-shaped rooms, add one row per rectangle.
- Coverage is the documented spread rate of the product you pick (the low end of the range on its data sheet) or the figure you type, and it applies to every coat. Data-sheet rates assume a smooth, sealed surface. Real coverage depends on the product, the surface texture and porosity, and how you apply the paint.
- Nothing is subtracted for skylights, light fixtures or vents.
- Walls, trim and primer are not included. Use the paint calculator for walls.
- Cans are rounded up to whole containers of the size you choose; the calculator does not mix gallon and quart cans.
Frequently asked questions
How do I measure a vaulted or sloped ceiling?
Measure along the slope, not across the floor. For a simple pitched ceiling, measure from the wall to the ridge along the ceiling surface for each side, multiply each by the room length, and add each side as a separate row.
Is ceiling paint coverage different from wall paint?
It can be, so use the spread rate of the ceiling paint you buy. For example, Benjamin Moore lists 400–450 sq ft per gallon for its Waterborne Ceiling Paint and Sherwin-Williams lists 350–400 for ProMar Ceiling Paint. Pick your product in the calculator or type the coverage printed on your can.
Can I paint walls and ceilings with the same can?
Only if you use the same paint for both. In that case, add the result of this calculator to the paint calculator’s result before you round up to whole cans.
Sources
- Waterborne Ceiling Paint Ultra Flat (N508) Technical Data Sheet — Benjamin Moore. Ceiling paint: "Spread Rate Per Gallon 400 – 450 Sq. Ft." (preset uses 400).
- Speedhide Interior Latex Flat (6-70 Series) Technical Data — PPG. Walls and ceilings: "Approximately 400 sq. ft. (37 sq. meters) per U.S. Gallon (3.78L) on smooth, nonporous surfaces."
- ProMar Ceiling Paint Flat (A27W05050) Product Data Sheet — Sherwin-Williams. Ceiling paint: "Coverage: 350-400 sq. ft. per gallon" (preset uses 350).
- Harmony Product Data Sheet — Tikkurila. Walls and ceilings: "Theoretical coverage 8-12 m²/l." (preset uses 8).
- NIST Handbook 44, Appendix C – General Tables of Units of Measurement — National Institute of Standards and Technology. Exact unit definitions: 1 in = 2.54 cm, 1 yd³ = 27 ft³, 1 US gal = 231 in³, 1 lb = 0.45359237 kg.
Method reviewed November 2, 2026