Ceilings are the easy part of a paint estimate. There are no doors to subtract and no height to multiply: you need the floor’s length and width, and nothing else.
Ceiling area = room length × room width
Gallons = ceiling area × coats ÷ coverage per gallon
A 12 × 14 ft ceiling
The ceiling covers 168 sq ft. At 375 sq ft per gallon and one coat that is 0.45 gal, so the buy quantity is 1 gallon. With two coats the calculation rises to 0.9 gal and still rounds to 1 gallon.
This example assumes
- 375 sq ft per gallon
- One coat unless stated
- No extra allowance
Why small ceilings round to a quart
The planner follows the way paint is sold in the US: a quart for up to a quarter of a gallon, a gallon up to one gallon, and whole gallons above that. That makes the cut-off visible in real rooms:
| Ceiling | Calculated (1 coat) | Buy |
|---|---|---|
| 8 × 10 ft | 0.21 gal | 1 quart |
| 10 × 10 ft | 0.27 gal | 1 gallon |
| 12 × 14 ft | 0.45 gal | 1 gallon |
| 15 × 20 ft | 0.8 gal | 1 gallon |
A ceiling only just over a quarter gallon needs a full gallon, so a tiny difference in size changes what you carry out of the store. In metric mode the planner shows the minimum volume instead, because can sizes vary by market.
What changes the estimate?
- The coverage on your ceiling paint can, which is often a different product from wall paint
- Texture: popcorn or heavy texture soaks up more paint than a smooth ceiling
- Coats: a new color or bare drywall can need more than one
- A primer coat, which has its own coverage
- Whether you are also painting the walls, since the planner adds ceiling and wall paint as separate lines
If you are painting the walls too, the room guide covers the wall side, and the planner keeps both on one list.