Subtracting openings improves a paint estimate, but false precision can waste more time than material. Measure large openings; ignore tiny interruptions.
Use width × height
A typical door measuring 3 × 7 ft removes 21 sq ft from the wall area. A 3 × 5 ft window removes 15 sq ft. Multiply by the number of identical openings.
Keep casing and trim separate
The opening area does not include the casing or jamb if those are being painted. Trim is usually estimated by linear length and may use a different paint and sheen.
Stay conservative
Do not subtract outlets, vents, or small fixtures. Their combined area is small and the retained allowance helps with roller and tray losses.
Practical takeaway
Subtract meaningful unpainted surfaces, then let the waste allowance cover small interruptions and application losses.
Related paint guides
Calculate paint separately for each colour and finish
Group paint areas by the exact product, colour and finish before rounding cans. Use a worked example to avoid a misleading whole-house total.
How to measure a room for paint
Measure wall perimeter, height, ceilings, doors, and windows for a paint estimate you can audit.
How much paint does a gallon cover?
Compare gallon, five-gallon, quart, and litre paint coverage, then adjust label area for coats, porosity, and waste.