Paint Calculator
For new walls or dramatic color changes, add 1 coat of primer before painting.
This tool is part of these guided projects. Each project provides step-by-step instructions with checklists and all the tools you need in one place.
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Estimate primer gallons from surface area and substrate type. Calculate stain-blocking, drywall, and masonry primer for proper paint prep coverage rates.
Calculate wallpaper rolls from room dimensions and roll size. Account for pattern repeat, waste, and drops for single and double roll coverage estimates.
Estimate deck stain gallons from deck square footage and board type. Calculate semi-transparent or solid stain for rails, steps, and horizontal decking.
Sum four walls minus doors and windows. Add ceiling area if painting overhead.
Wall Area = 2 × (L + W) × Height − Openings; Ceiling = L × WStandard latex: 350–400 sq ft/gallon per coat on smooth surface. Textured walls reduce coverage 10–20%.
Gallons = (Area × Coats) ÷ Coverage per GallonNew drywall and dark color changes need primer coat. Primer covers less area than finish paint.
Primer Gallons = Area ÷ Primer Coverage (250–350 sq ft/gal)Updated: July 2026
Wall area ~448 sq ft minus 60 sq ft openings = 388 sq ft × 2 coats ÷ 375 = 2.1 gal → 3 gallons.
800 × 2 coats ÷ 400 = 4 gallons finish. One gallon primer for color change from dark to light.
300 sq ft ceiling ÷ 350 = 0.86 gal — buy 1 gallon flat ceiling white.
Estimate interior or exterior paint gallons before buying at the store. Enter room dimensions, number of coats, and paint coverage (typically 350–400 sq ft per gallon) to get separate wall and ceiling quantities plus primer needs.