How Much Paint for a Room: Gallons Needed by Room Size and Coat Count
A standard 12×12 room with 8-foot ceilings has approximately 448 square feet of wall area and needs 1.5 gallons for one coat or 3 gallons for two coats. One gallon of paint covers 350 to 400 square feet per coat on smooth walls. How much paint for a room depends on wall area (length plus width times 2 times ceiling height, minus doors and windows), the number of coats, and whether the surface is previously painted or raw drywall, which absorbs significantly more paint per coat.
Buying too little paint means a mid-project store run that risks a color dye-lot mismatch. Buying too much wastes $50 to $150 on paint that sits in your garage until disposal. The calculation is not complicated; it just requires measuring the room before you go shopping.
Enter room length, width, ceiling height, number of doors and windows. The paint calculator gives you gallons per coat and total for two coats.
Open the Paint Calculator →The Paint Coverage Formula
Step 1: Calculate wall area. Wall area = 2 x (Length + Width) x Ceiling Height. Step 2: Subtract openings. Each standard door removes 21 square feet; each standard window removes 15 square feet. Step 3: Divide by coverage rate. One gallon covers 350 to 400 square feet per coat. Round up to the nearest half-gallon.
Example for a 10×14 room at 8-foot ceilings with 1 door and 2 windows: Wall area = 2 x (10+14) x 8 = 384 sq ft. Subtract door (21) and two windows (30) = 333 sq ft. At 350 sq ft per gallon: 0.95 gallons per coat. Round up to 1 gallon per coat, 2 gallons for two coats. For the full interior painting cost alongside your material estimate, our guide on cost to paint a house interior covers professional vs DIY pricing. For whether one coat is enough in your situation, our one coat vs two coats guide explains when you can skip the second coat and when you cannot.
Paint Gallons by Room Size and Coat Count
| Room size | Net wall area | 1 coat (gal) | 2 coats (gal) | Recommended purchase |
|---|---|---|---|---|
| 8×8 (small bedroom) | 220 sq ft | 0.7 | 1.4 | 1 gal for 1-coat; 2 gal for 2-coat |
| 10×10 | 264 sq ft | 0.8 | 1.6 | 1 gal for 1-coat; 2 gal for 2-coat |
| 10×12 | 296 sq ft | 0.9 | 1.8 | 1 gal for 1-coat; 2 gal for 2-coat |
| 12×12 (standard) | 320 sq ft | 0.9 | 1.8 | 1 gal for 1-coat; 2 gal for 2-coat |
| 12×16 (master bedroom) | 384 sq ft | 1.1 | 2.2 | 1 gal for 1-coat; 3 gal for 2-coat |
| 14×18 (large room) | 448 sq ft | 1.3 | 2.6 | 2 gal for 1-coat; 3 gal for 2-coat |
| 16×20 (great room) | 576 sq ft | 1.6 | 3.3 | 2 gal for 1-coat; 4 gal for 2-coat |
| 20×20 (open concept) | 672 sq ft | 1.9 | 3.8 | 2 gal for 1-coat; 4 gal for 2-coat |
Adding Ceiling Paint
Ceiling paint is calculated separately: simply measure room length x width. Ceiling paint is generally flat-finish and a different product from wall paint (walls use eggshell or satin; ceilings use flat white). Coverage is the same: 350 to 400 sq ft per gallon per coat. Most ceilings get two coats when they are being repainted from white to white, or when covering water stains. A 12×12 ceiling = 144 sq ft. Two coats: 288 sq ft / 350 = 0.82 gallons. Buy 1 gallon for a 12×12 ceiling at two coats, with leftover for touch-ups.
New Drywall vs Repainting: Coverage Difference
Raw, unprimed drywall absorbs significantly more paint per coat than previously painted walls because the drywall compound and paper face are porous. On new drywall, expect coverage closer to 250 to 300 sq ft per gallon on the primer coat. Always prime new drywall before applying finish paint: this seals the surface and allows the finish paint to cover at its rated 350 to 400 sq ft per gallon. Skipping primer on new drywall produces blotchy coverage, visible lap marks, and higher overall paint consumption because you need 3 to 4 coats instead of 2 to achieve uniform sheen. Primer is cheaper per gallon than finish paint, so priming is always economical on new drywall.
Three Real Rooms Calculated
Example 1: Standard bedroom repaint in Nashville, Tennessee
A homeowner repainting a 12×14 bedroom with 9-foot ceilings, 1 door, 2 windows. Wall area: 2 x (12+14) x 9 = 468 sq ft. Minus door (21) and two windows (30) = 417 sq ft. At 375 sq ft per gallon: 1.11 gallons per coat. Two coats: 2.22 gallons. Purchased 2.5 gallons (two 1-gallon cans and one quart) of premium eggshell paint at $56/gallon. Total paint cost: $126 plus a quart at $18. Ceiling: 12×14 = 168 sq ft, 1 coat of flat white ceiling paint: 0.48 gallons, purchased 1 quart ($12). Total paint: $156.
Example 2: Open-concept living area in Austin, Texas
A homeowner painting a 22×28 open-concept living and dining area with 10-foot ceilings, 3 doors, 6 windows. Wall area: 2 x (22+28) x 10 = 1,000 sq ft. Minus 3 doors (63) and 6 windows (90) = 847 sq ft. At 350 sq ft per gallon: 2.42 gallons per coat. Two coats: 4.84 gallons. Purchased 5 gallons in one 5-gallon bucket (cheaper per gallon than single gallons). Cost at $42/gallon in a 5-gallon pail: $210. The 5-gallon bucket also eliminated any dye-lot variation risk since all paint was mixed from one batch.
Example 3: New construction bedroom in Denver, Colorado
A homeowner painting a new construction 13×15 bedroom with 8-foot ceilings, raw drywall. Wall area: 2 x (13+15) x 8 = 448 sq ft. Minus 1 door (21) and 1 window (15) = 412 sq ft. For new drywall: 1 gallon drywall primer (covers 300 sq ft, needed 1.5 gallons – purchased 2 gallons). After priming, 2 coats of finish paint: 412/375 = 1.1 gallons per coat x 2 = 2.2 gallons. Purchased 3 gallons of finish. Total primer + finish: 5 gallons total versus the 2.5 gallons needed for the same room repaint. New construction always uses approximately double the paint of a repaint job.
Enter your room dimensions and coat plan. The paint calculator also gives you the cost estimate at your local price per gallon.
Calculate Paint Gallons →Frequently Asked Questions About Paint Coverage
How much paint do I need for a 12×12 room?
A 12×12 room with 8-foot ceilings has approximately 320 to 350 square feet of net wall area after subtracting one door and one window. You need about 0.9 to 1 gallon per coat. For two coats (standard for most repaints): purchase 2 gallons. For new drywall, add 1 to 2 gallons of primer before the finish coats.
How many square feet does one gallon of paint cover?
One gallon of interior wall paint covers 350 to 400 square feet per coat on previously painted, smooth walls. On new drywall or heavily textured walls, coverage drops to 250 to 300 square feet per gallon. Premium paints with higher pigment loads tend to provide better coverage at the rated 350 to 400 sq ft range than budget paints, which often require an extra coat to achieve uniform coverage.
Should I buy paint in gallons or a 5-gallon bucket?
A 5-gallon bucket is typically $40 to $50 per gallon versus $45 to $65 for individual gallons of the same paint, making it 10 to 25 percent cheaper. The 5-gallon bucket also eliminates dye-lot variation between cans, which can cause visible color inconsistencies on large walls. Buy a 5-gallon bucket when you need 3 gallons or more. For smaller projects (one or two rooms), individual gallons allow you to buy exactly the amount you need without waste.
How do I calculate paint for a room with vaulted ceilings?
For rooms with vaulted ceilings, measure the actual wall height at each point: measure the standard height walls normally (height x width x 2), then calculate the triangular vaulted sections separately (base x height / 2 for each triangular gable). Add all sections together for total wall area. Vaulted ceilings significantly increase wall area and paint quantity compared to standard 8 to 9-foot flat ceilings.
How much paint for a bedroom including ceiling?
For a standard 12×12 bedroom at 8-foot ceilings: approximately 2 gallons for walls (two coats) plus 1 gallon for ceiling (two coats) = 3 gallons total. Buy the wall paint and ceiling paint separately as they are different products: eggshell or satin sheen for walls, flat white for ceilings. Most major paint brands sell ceiling paint specifically formulated to minimize roller stipple marks that are visible on horizontal surfaces.
What is the best way to avoid running out of paint mid-project?
Calculate your square footage accurately before buying, then add 10 percent as a buffer. For a calculated need of 2 gallons, buy 2.5 gallons. More importantly, buy all cans from the same mixed batch or dye lot: different batches of the same color can have subtle variations that are visible on a large wall. If you run out and buy more, have the new can blended with the remaining old paint to minimize the transition line.
Do I need to prime before painting?
Always prime: new drywall (required, the paper face is absorbent), when changing from a dark color to a light color (tinted primer dramatically reduces the number of finish coats needed), when covering stains (shellac-based primer for water stains, oil stains, or smoke damage), and when painting previously unpainted wood or metal. Repainting the same color or a similar-toned color over an existing finish in good condition is the main scenario where primer can be skipped.
How long does leftover paint last in storage?
Latex paint stored in a properly sealed can at room temperature lasts 2 to 10 years. Keep the lid sealed tightly by tapping it down around the full circumference, store the can upside down to prevent a skin from forming on top, and keep it in a climate-controlled space (not a garage that freezes in winter, as latex paint is permanently damaged by freezing). Label the can with the room name and purchase date for future touch-ups.
Related Calculators and Guides
For paint VOC limits and indoor air quality guidance, the EPA Indoor Air Quality VOC guidance provides authoritative standards for low-VOC and zero-VOC paint selection for bedrooms and living spaces where ventilation is limited.