Paint Coverage Calculator Guide: How Much Paint to Buy for Any Room or Surface
One gallon of paint covers approximately 350–400 sq ft per coat. Learn the formula for walls, ceilings, and trim — including deductions for windows and doors.
The Paint Coverage Formula
The fundamental formula works for walls, ceilings, and trim separately, then combines them. Always calculate by surface type since coverage rates, sheen choices, and number of coats differ. For walls: Paintable area = (Room perimeter × Wall height) − (Doors × 20 sq ft) − (Windows × 15 sq ft). For ceilings: Area = Length × Width. For trim (baseboard
Coverage Rates by Surface Type
Coverage varies significantly based on surface porosity, texture, and paint quality. Always use the manufacturer's stated coverage on the can as your primary reference — use 350 sq ft/gallon as a safe default when the can isn't available. Differences in practice: smooth drywall with good primer base: 400–450 sq ft/gallon. Standard primed drywall: 3
When to Prime: The One-Coat vs Two-Coat Question
Priming is critical for: new drywall (paper facing is highly porous — skip primer and you'll need 3+ coats of topcoat), drastic color changes (white to dark color or vice versa), stain blocking (water damage, smoke, crayon), painting over glossy surfaces (primer improves adhesion), and bare wood or plaster. For standard repaints (existing painted s
Choosing the Right Sheen
Paint sheen (finish) affects both appearance and durability. Higher sheen = more durable and washable but shows surface imperfections more clearly. Flat/Matte: ceiling paint standard, hides imperfections, not washable — for low-traffic areas only. Eggshell: slight sheen, good for living rooms, bedrooms — most popular interior finish. Satin: more wa
Frequently Asked Questions
How many gallons of paint do I need for a 12×12 room?
A 12×12 room with 8' ceilings: perimeter = 48 ft. Wall area = 48×8 = 384 sq ft. Subtract 1 door (20) + 1 window (15) = 349 sq ft net. One coat: 1 gallon exactly. Two coats: 2 gallons. Ceiling: 12×12 = 144 sq ft → 1 quart per coat. Total for walls + ceiling, 2 coats: approximately
Does paint color affect how many coats you need?
Yes. Dark colors over light, or light over dark, typically require 2–3 coats. Same color refreshes (same color on painted surface) may be achievable in 1 coat. High-hiding paints with titanium dioxide pigment cover in fewer coats. Pure yellows, oranges, and reds are notorious for
What is the difference between interior and exterior paint?
Exterior paint contains higher levels of UV-resistant pigments and flexible binders (resins) that expand and contract with temperature changes without cracking. It also includes mildewcides and is more moisture-resistant. Exterior paint should never be used indoors — the VOCs (vo
How do I match paint to an existing color?
Most hardware stores (Home Depot, Lowe's, Sherwin-Williams) offer spectrophotometric color matching from a paint chip, fabric swatch, or small painted sample. Bring a 3×3 inch sample minimum for best results. For existing wall paint, cut out a 2×2 inch section of drywall behind a
Can I mix leftover paint?
Same brand, same type (latex/oil), same sheen: generally yes, if the colors are similar enough. Mix thoroughly in a large bucket (called 'boxing') to ensure color consistency. Dramatically different colors will produce muddy results. Never mix latex and oil-based paints. Leftover