Ceiling Paint Calculator
Work out how much ceiling paint you need from the room size, number of coats and coverage, including sloped and cathedral ceilings.
Enter the room size and this calculator works out the ceiling area, including sloped or cathedral ceilings, and how much paint the number of coats you plan will need. It rounds the estimate up to a shopping quantity; choose available cans or tins that cover that amount.
How to use this tool
- Choose feet and US gallons, or metres and litres.
- Enter the length and width of the room, measured wall to wall.
- Pick the ceiling shape: flat, or the pitch of a sloped or cathedral ceiling.
- Set the number of coats, the coverage from the paint label and an extra allowance.
Formula
Paint = length × width × slope factor × coats × (1 + extra %) ÷ coverage
For a ceiling that rises r inches for every 12 inches across, the slope factor is √(1 + (r ÷ 12)²): 1.118 at 6/12 and 1.414 at 12/12. Coverage is the area one gallon or litre covers in one coat, often 350–400 sq ft per gallon or around 10–13 m² per litre on a smooth, primed surface. Rough or textured ceilings soak up noticeably more, so lower the coverage figure for them.
Example
A 14 × 12 ft bedroom has a 168 sq ft flat ceiling. Two coats at 350 sq ft per gallon with no extra need 168 × 2 ÷ 350 = 0.96 gallons, so a single gallon does it. With the default 10% extra the figure is 1.06 gallons, and the calculator suggests a gallon plus a quart.
Frequently asked questions
Should I use ceiling paint or wall paint?
Ceiling paints are usually flat and made to spatter less when rolled overhead, and a flat finish hides small flaws. Wall paint works too, but any sheen tends to show roller marks when light hits the ceiling at a low angle.
How many coats does a ceiling need?
Two coats is the norm for new drywall (after primer) or a colour change. Refreshing a clean ceiling with the same white can often be done in one coat.
Does this include primer?
No. New drywall, water stains and smoke marks normally need a coat of stain-blocking or drywall primer first. Work that out separately using the primer’s own coverage figure.
Is the ceiling area the same as the floor area?
For a flat ceiling, yes. A sloped ceiling has more surface than the floor below it, which is why the slope factor is applied.
Last updated: 2026-10-30