Paint Calculator — How Much Paint Do I Need?
Calculate exactly how many gallons you need and what it'll cost. No more guessing or extra trips to the store.
Painting multiple rooms the same color? Enter how many.
Your Paint Estimate
Cost Estimate
⭐ Gear That Makes a Paint Job Look Pro
Most homeowner paint jobs look amateur because of the tools, not the paint. These three upgrades are the difference between rolling stripes and a clean finish.
Premium Microfiber Roller Covers
Cheap roller covers shed fibers into the finish and leave stipple marks. Step up to a 3/8-inch microfiber roller from Wooster or Purdy and the wall finishes smoother in one coat than two coats with a budget cover. Buy a 6-pack — you'll use them.
View on Amazon →Painter's Tape Plus Drop Cloth Set
True blue painter's tape (14-day clean release) is the only kind that pulls off without taking paint with it. Pair it with canvas drop cloths — not plastic, which slips — for cleaner lines and zero floor damage. A good kit lasts years.
View on Amazon →Airless Paint Sprayer (for whole rooms or exteriors)
If you're painting more than two rooms or any exterior, an airless sprayer pays for itself in time saved. Look for one with adjustable pressure (250-3000 PSI) and a reversible tip — it'll handle everything from primer to thick exterior paint and cleans up in 10 minutes.
View on Amazon →As an Amazon affiliate, HomeCalc Tools earns a small commission if you purchase through these links — at no extra cost to you. We only recommend products we would actually use ourselves.
How Much Paint Do I Need?
The amount of paint you need depends on room size, number of coats, and wall surface texture. As a quick rule: one gallon covers 350-400 sq ft of smooth wall per coat. A standard 12x12 room with 8-foot ceilings needs about 1.5 gallons for two coats. Always buy a little extra for touch-ups — unopened paint can be returned, and leftover paint is useful for years.
Interior Painting Cost in 2026
DIY painting costs $50-$150 per room for paint and supplies. Professional painters charge $300-$800 per room, or $2-$4 per square foot of wall area. A whole-house interior (3 bedroom, 2 bath) typically runs $1,500-$4,000 for professional work. The biggest cost factors are room count, ceiling height, and how much prep work (patching, sanding, priming) is needed.
How Many Coats of Paint Do I Need?
Two coats is the standard for most projects and gives the best finish. You might get away with one coat if you're repainting the same color with a high-quality paint-and-primer combo. Use three coats when making a dramatic color change (especially going from dark to light), painting over a bold color like red or deep blue, or covering bare drywall or patched areas.
Tips to Save Money on Paint
Buy during holiday sales — Memorial Day, Labor Day, and Black Friday typically see 25-40% off at major retailers. Consider "oops paint" or mistinted gallons at Home Depot and Lowe's for $5-$10 per gallon (great if you're flexible on color). Mid-range paints like Behr Marquee or Sherwin-Williams Emerald offer excellent coverage in fewer coats, actually saving money over cheap paint that needs 3 coats.
How Much Paint Do You Really Need?
The number our calculator gives is for the actual square footage you're painting. To convert that to gallons you should buy, divide by the paint's stated coverage rate (typically 350-400 sq ft per gallon for one coat on a primed wall, less on textured or porous surfaces). Then multiply by the number of coats, and add 10% for cutting in, trim, and unavoidable waste. Most homeowners under-buy on the first trip and over-buy on the second because they can't remember the exact color. Save the can lid or take a photo of the formula sticker before you leave the store.
Why Two Thin Coats Always Beats One Thick Coat
A common amateur mistake is loading the roller heavy to "save time." It creates drips, uneven coverage, and a finish that takes a week to fully cure. Two thin coats — with light sanding between — gives you a tighter, more durable finish that resists scuffs and washes clean for years. This matters more in high-traffic areas like hallways and stairwells than in bedrooms. If you're going from a dark color to a light one, prime first; otherwise you'll be on coat three trying to hide the old color.