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
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?
Understand label coverage, surface porosity, colour changes, and why exact paint volume differs from cans to buy.
Do I need one coat or two?
Choose a realistic coat count based on colour change, surface condition, sheen, and product instructions.