Contractor Paint Coverage Calculator

Frequently Asked Questions

How much area does one gallon of paint cover?

A gallon of interior paint covers about 350–400 sq ft per coat on a smooth, primed surface. Rough textures (stucco, popcorn ceilings, masonry) drop coverage to 200–250 sq ft. Always plan for two coats on color changes or new drywall.

How do I subtract doors and windows from my paint estimate?

Standard interior door = 21 sq ft. Standard window = 15 sq ft (3×5). Subtract these from your gross wall area only if you have many openings - for one or two openings per room, the savings is within rounding error and you risk running short.

Do I need primer?

Yes when painting bare drywall, switching from dark to light, painting over stains, or applying water-based paint over oil. Modern paint-and-primer-in-one products work for repaints in similar colors but do not replace dedicated primer for new construction or major color changes.

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Estimates for informational purposes only.

Important Disclaimer: Estimates for informational purposes only.

This calculator provides estimates for informational purposes only. Results are based on assumptions and may not reflect actual outcomes. Consult qualified professionals in relevant fields before making important decisions based on these results.

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How This Calculator Works

The calculator multiplies the room perimeter by ceiling height to get total wall area, subtracts openings (doors at ~21 sq ft each, standard windows at ~15 sq ft), multiplies by your coat count, and divides by paint coverage to find gallons. Rounding to the nearest quarter-gallon matches retail can sizes (1-quart, 1-gallon, 2-gallon, 5-gallon) so you can buy in real-world increments.

Coverage Rules of Thumb

350 sq ft/gallon - Smooth drywall, eggshell or satin finish, previously painted in similar color. Default.

300 sq ft/gallon - Lightly textured walls, flat finish, or going lighter color over darker.

250 sq ft/gallon - Heavy texture (knock-down, popcorn ceiling), bare drywall, or going dark over light without primer.

200 sq ft/gallon - Masonry, stucco, brick, or unprimed wood. Plan two coats minimum.

Primer vs Paint & Coats

For most repaints in similar colors, 2 coats of self-priming paint over a clean surface is sufficient. Use a separate tinted primer when: covering deep stains (smoke, water, marker), bare drywall or wood, going from dark to light (saves a coat or two of finish paint), or switching between latex/oil. Tinted primer in a shade close to your topcoat dramatically reduces the coats needed for deep colors like navy, charcoal, or red.

Quality Tiers and What to Expect

Budget paint ($20-25/gallon Behr/Glidden): adequate for closets, garages, low-traffic. Mid-range ($35-50/gallon Sherwin-Williams ProClassic, Behr Marquee): standard residential, washable, good color depth. Premium ($60-90/gallon Benjamin Moore Aura, Sherwin Emerald): single-coat coverage in most colors, superior wash-ability, near-zero VOC - actually cheaper per square foot once you account for needing fewer coats and less labor.

Don't Forget the Trim & Ceiling

This calculator covers walls only. Add: ceiling paint (use a separate flat ceiling paint, typically 1 gallon per 400 sq ft) and trim paint (1 quart covers all baseboards plus door casings in a typical 12'x12' room). Trim paint should be semi-gloss for durability. Doors and window sashes are often painted but require 24+ hours dry time before re-installing hardware.

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