How much paint do I need? Enter your room dimensions and coat count to calculate exactly how many gallons of paint to buy, with coverage estimates and cost.
Ready to calculate
Enter your room dimensions
Last updated March 31, 2026 by our expert review team
350-400
sq ft/gal · Interior walls
400-450
sq ft/gal · Trim & doors
300-350
sq ft/gal · New surfaces
Cherry Jane Limbago
Licensed Civil Engineer & Master Plumber
Licensed civil engineer and master plumber with 10+ years in structural design, estimation, and project management. Currently Project Engineer at Universal Robina Corporation.
See full profileHawkin
Certified Cost & Estimating Professional
AACE-certified estimator working with 20+ insulation companies including the two largest franchises in America.
See full profileUpdated March 2026
How we verify our calculatorsPer gallon on smooth, previously painted walls. Textured or bare surfaces reduce coverage 15-25%.
Hides flaws, easy touch-up
Subtle sheen, washable
Wipes clean from grease
Resists moisture
Durable, cleans easily
No glare, hides marks
Buy all your gallons at once and have the store shake them together. Same color code can shift slightly between batches.
Cut in edges with a 2.5" angled brush before rolling. Rolling first leaves visible lap marks at corners.
Use a bonding primer (Zinsser or Kilz) on glossy surfaces, dark colors, or fresh drywall. Without it, your topcoat peels within a year.
Painting new construction or fresh walls? Use our drywall calculator to estimate sheets before painting new walls.
Considering wallpaper instead? Our wallpaper calculator estimates rolls, strips, and paste for any room.
Roll in a W pattern across 3-4 foot sections, then fill in. Straight parallel strokes leave streaky lines.
Paint when humidity is below 50% and temps are 50-85°F. High humidity causes bubbling, cold temps prevent adhesion.
Finishing a deck or fence too? Use our stain calculator to figure out how much stain you need for exterior wood.
Wall height times room perimeter gives you total wall area. We subtract 20 sq ft per door and 15 per window, then divide by 375 sq ft/gallon (slightly conservative vs. the 350-400 on the can label).
The 10% buffer covers touch-ups, cut-in overlap, and paint left in the tray and roller. Textured walls, dark colors, or bare surfaces? Add 15-20% more.
Formula
(Wall Height × Perimeter - Doors × 20 - Windows × 15) × Coats ÷ 375 = Gallons
How much paint do I need?
Multiply wall perimeter by ceiling height, subtract 20 sq ft per door and 15 per window, then divide by 350-400. A 12x12 room needs about 2 gallons for two coats.
How many gallons for a room?
10x12 bedroom: 2 gallons. 15x20 living room: 3-4 gallons. Bathroom: 1-2 gallons. All assume two coats at 350-400 sq ft per gallon.
How many sq ft does a gallon cover?
350-400 on smooth walls. Drops to 250-300 on textured, new drywall, or bare wood. Semi-gloss covers slightly less (300-350).
One coat or two?
Almost always two. One coat leaves thin spots visible in side lighting. Only skip on exact same-color recoats.
When do I need primer?
New drywall, raw wood, patched spots, dark-to-light changes, and glossy surfaces. Zinsser and Kilz are the go-to brands.
What's the difference between finishes?
Flat hides flaws but scuffs. Eggshell is most popular. Satin for kitchens. Semi-gloss for trim and bathrooms. More sheen = more durable.
How much does it cost to paint a room?
DIY: $50-150. Pros: $2-6/sq ft ($300-800 bedroom, $800-2,500 living room). See our paint cost calculator for a full budget breakdown.
Is expensive paint worth it?
For high-traffic areas, yes. Benjamin Moore Regal ($50-80/gal) covers in fewer coats and lasts 5-7 years vs 2-3 for budget paint.
About 270 sq ft after subtracting a door and two windows. Two gallons covers two coats with touch-up left over. Eggshell is the go-to finish.
Use satin or semi-gloss for grease resistance. Budget an extra quart for trim and window frames.
Buy a 5-gallon bucket for color consistency. Tall ceilings show roller marks more, so use quality paint.
Skipping primer on new drywall
Mudded joints and paper-faced areas absorb paint differently, creating light and dark patches ('flashing'). One coat of PVA primer fixes this.
Painting in bad weather
Above 50% humidity: bubbling. Below 50°F: peeling. Check the forecast for 48 hours after painting, not just the day of.
Rolling before cutting in
Cut in one wall with a brush, then immediately roll it while the edges are still wet. If you roll first, the dried roller texture shows through your brush work.
Cheap roller covers
A $2 roller sheds fibers and leaves stipple marks. Spend $8 on a Purdy or Wooster microfiber. Use 3/8" nap for smooth walls, 1/2" for textured.
Leaving tape on too long
Pull tape within 1-2 hours of the final coat while it's still slightly tacky. After 24 hours, the adhesive bonds and tears the paint off in strips.
Buying the exact amount
Always grab one extra gallon. You can't always color-match mid-project, and the extra covers future touch-ups.
Important Disclaimer
These estimates are for planning purposes only. Actual costs vary by location, material availability, and project complexity. Always get at least 3 local quotes. This calculator does not replace professional advice.