Paint Calculator
Calculate how much paint you need for a room or project based on surface area and coverage rates.
Formula
Gallons Needed = (Total Paintable Area × Number of Coats) / Coverage Rate per Gallon. Standard coverage: 350-400 sq ft per gallon on smooth surfaces.
How to Use
- 1Calculate the total paintable surface area (wall perimeter × height, minus windows and doors).
- 2Determine the number of coats needed (typically 2 coats of finish, plus primer if needed).
- 3Check the paint manufacturer's coverage rate (typically 350-400 sq ft per gallon for smooth surfaces).
- 4Divide total area (× number of coats) by the coverage rate to get gallons needed.
- 5Round up to the nearest whole gallon and add 10% for touch-ups and waste.
Example
Scenario
You are painting a master bedroom that is 15×18 feet with 9-foot ceilings, two 3×5 foot windows, one 3×7 foot door, and a closet opening. Two coats of paint are needed with no primer.
Calculation
Wall perimeter: (15 + 18) × 2 = 66 linear feet. Wall area: 66 × 9 = 594 sq ft. Subtract openings: 2 windows (30 sq ft) + door (21 sq ft) = 51 sq ft. Net area: 594 - 51 = 543 sq ft. Two coats: 543 × 2 = 1,086 sq ft to cover. At 375 sq ft/gallon: 1,086 / 375 = 2.9 gallons.
Result
You need 3 gallons of paint for the walls (two coats). If painting the ceiling (270 sq ft, two coats), add 2 more gallons for a total of 5 gallons.
Tips
- ★Reduce coverage estimates to 250-300 sq ft per gallon for textured walls, porous surfaces, and dark-over-light color changes.
- ★Always buy an extra quart or half gallon for touch-ups — keeping the same batch ensures color consistency.
- ★Primer coverage rates are typically lower than paint (300-350 sq ft per gallon) — estimate primer separately.
- ★For spray application, increase material quantity by 20-30% compared to brush and roller due to overspray.
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Common questions about the paint calculator
One gallon of quality interior latex paint covers approximately 350-400 square feet per coat on smooth, previously painted surfaces. Coverage drops to 250-300 square feet per gallon on textured surfaces, new drywall (first coat), and when making dramatic color changes. Always check the manufacturer's coverage specification on the paint can.
Measure each wall at its tallest and shortest points, then average the two heights to get the effective wall height. For example, if one wall goes from 8 feet to 14 feet, use 11 feet as the height for that wall. Calculate the triangular gable area separately using (base × height) / 2.
Yes, always include ceiling paint as a separate line item. Ceiling paint is typically a flat finish white that covers approximately 400 square feet per gallon. Calculate ceiling area as room length × width. One coat is usually sufficient unless the ceiling is stained or changing from a dark to light color.