How many square feet does a gallon of paint cover?
Standard interior latex paint covers approximately 350–400 sq ft per gallon on a primed surface in a single coat. This calculator uses a conservative 350 sq ft/gallon for walls. Coverage drops significantly on rough, unprimed, or highly porous surfaces — account for this on new drywall or bare wood.
Should I plan for one coat or two?
For most residential interior work, two coats is standard. One coat is sufficient only when applying a similar colour with a premium paint over a well-primed, clean surface. New drywall, colour changes, dark-to-light transitions, and any stain coverage always require two coats minimum. This calculator lets you set your coat count per room.
How do I calculate paint for a room?
Add up the area of all walls (width × height for each), then subtract door openings (approximately 21 sq ft each) and windows (approximately 15 sq ft per standard window). Divide the net area by the coverage rate of your paint and multiply by the number of coats. This calculator handles all of that — enter your dimensions and let it do the math.
How much waste buffer should painters add?
A 10% waste buffer is standard for most residential interior jobs, covering roller waste, touch-ups, and uneven coverage. Use 15% for sprayed finishes, highly textured surfaces, or any job where you need to match an existing colour and waste is higher.
What is the coverage rate for exterior paint versus interior?
Exterior paints have similar theoretical coverage to interior (350–400 sq ft/gallon) but real-world coverage is often lower due to rough siding, weatherboard profiles, and wind waste when spraying. For exterior cladding, estimating 300–350 sq ft/gallon is more realistic. Add 15% waste as a minimum on exterior jobs.
