Example: a 20 × 15 ft flat ceiling
Area is 300 ft², approximately 27.871 m². Two coats and an illustrative 10% allowance create 660 ft² of coverage demand. At an assumed 350 ft² per US gallon, 660 ÷ 350 = 1.8857 gallons, so the calculator reports two gallons. The assumed coverage is not a claim about a particular paint.
Start with the painted surface
A flat ceiling generally shares the room’s plan dimensions, but a vaulted surface has more area than its horizontal footprint. Measure each actual plane from a drawing or a safe survey method. Divide stepped ceilings into their horizontal and vertical faces and keep soffit sides visible in the sketch.
Only deduct surfaces that will not receive this paint. A ceiling opening should be treated according to the actual finished surface, while a light fitting may leave almost no meaningful unpainted area. Avoid spending time on tiny deductions that are smaller than your measurement uncertainty.
Read coverage as a product input
Use the coverage basis stated for the selected ceiling paint and the surface condition. A previous wall-paint estimate is not automatically the right rate for this product. Keep colour, sheen and product code with the number so the same ceiling area can be repriced or recalculated if the specification changes.
The BEHR calculator separates ceiling and other painting tasks. That distinction is useful even when one product is used in several places: separate surface records show why a later change to walls does not change the ceiling quantity.
Apply coats and allowance only once
If coverage is stated for one coat, multiply the surface by the intended coat count. If a supplier has instead given a complete-system yield, establish whether coats are already included before using it. The coat count is an input from the planned work, not something the quantity result chooses.
Surface texture, application loss and touch-up stock should be discussed explicitly. Use an allowance appropriate to that documented scope; the example percentage below is only arithmetic. Do not inflate both the room length and the waste field to cover the same uncertainty.
Translate the result into local containers
This English calculator rounds purchases to whole US gallons. Metric dimensions do not turn that rounded purchase unit into litres. One US gallon equals 3.785411784 litres; use the product’s actual local container size when making a shopping list.
Separate primer, repairs and final ceiling paint. If the work is spread across several rooms with the same product and colour, combine their calculated needs before final package ordering. Keep any opened paint that remains usable as a separate stock credit rather than assuming a full can remains.
Do it in order
- Measure each ceiling face actually receiving paint.
- Record product coverage and its coat basis.
- Enter coats and allowance once.
- Round to the selected product’s available container sizes.
Planning boundary
Coverage estimates do not specify preparation, coating compatibility or the required number of coats.
Sources checked
Does the room paint calculator include this ceiling?
The interior-wall tool and the ceiling tool are separate. Check the scope of your existing estimate before adding another line.
Can I use the floor area for a vaulted ceiling?
Use the actual sloped surface area. A footprint alone omits the extra surface created by the slope.