Paint Calculator: Room Coverage & US Gallons
Estimate paint gallons for room walls and optional ceilings with doors and windows deducted, multiple coats, product coverage and extra allowance. All measurements use US customary units. Defaults are examples; use actual site dimensions and product coverage.
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Results
Results update live as you type. Estimates only — not financial, tax, or investment advice.
The Formula
Paint gallons = ((2 × (length + width) × height − opening area + optional ceiling area) × coats × (1 + extra% ÷ 100)) ÷ coverage
Understanding the Paint Calculator: Room Coverage & US Gallons
Example: a 12 × 10 foot room with 8 foot walls has 352 square feet of wall area. Subtract 42 square feet of doors and windows to get 310. Two coats at 350 square feet per gallon with 10% extra require 1.95 gallons, rounded up to two 1-gallon cans.
Enter decimal feet: 8 feet 6 inches is 8.5 feet. Add together the areas of doors and windows you will not paint. Coverage is per coat; use the product label for your surface and application method. The ceiling option assumes the same paint, coats and coverage. Calculate separately if the ceiling uses another product.
Example opening deduction: one 3 × 7 foot door (21 square feet) and a combined 21 square feet of windows total the default 42 square feet. Measure actual openings; trim painted separately should not be included in these wall estimates.
Frequently Asked Questions
Does this include primer?
No. Estimate primer separately using its own coat count and label coverage. Texture, porosity and color changes can change actual coverage.
Is the result gallons or cans?
The gallons result is the unrounded estimate. The can count rounds up to whole 1-US-gallon cans; it does not optimize quart or 5-gallon container purchases.