350 sq ft/gal assumes smooth drywall. Knockdown texture drops you to 280-300, orange peel to 250-280, popcorn ceilings to 200-230. Check your surface before trusting the spec.
Paint Calculator: Gallons for Walls, Ceilings & Trim
Estimate interior paint gallons for any room - walls, ceiling, openings subtracted, multiple coats applied.
Default settings
- Default coverage is 350 sq ft per gallon per coat, equivalent to about 8.59 sq m per liter per coat.
- Default overage is 10% to protect against touch-ups, texture, and small measurement misses.
- Openings are entered as one combined area instead of itemized door and window geometry.
- Results are planning estimates. Always confirm the final spread rate on the exact paint product.
How this estimate works
- Wall area = 2 x (length + width) x ceiling height
- Optional ceiling area = length x width
- Paintable area = wall area + ceiling area - openings area
- Raw paint = paintable area x coats / coverage
- Recommended paint = raw paint x (1 + overage percent)
- Buy quantity rounds up to the next quarter gallon equivalent
Related pages
Use a guide if coverage or units need a closer look.
Paint coverage per gallon guideUse this when you need to sanity-check the default 350 sq ft coverage setting.How these estimates workSee how unit switching, rounding, and default settings are handled across the calculators.Imperial and metric conversion guideCheck common feet, inches, meters, and centimeters mistakes before adjusting room inputs.Flooring calculatorCompare paint planning with another room-based material estimate.
FAQ
Quick answers if you need them.
Why does this tool ask for openings as one total area?
It keeps the estimate quick. Add doors and windows as one total if needed.
Why round up to quarter-gallon equivalents?
Paint is bought in practical package sizes. The estimate rounds up to avoid under-ordering.
How the paint estimate is calculated
The math behind the gallons number.
- Wall area = 2 x (length + width) x ceiling height. A 12 x 14 ft room at 8 ft ceilings is 2 x 26 x 8 = 416 sq ft.
- Ceiling area (optional) = length x width. Added only if you choose to paint the ceiling.
- Paintable area = wall area + ceiling area − openings area (doors and windows combined).
- Raw paint = paintable area x coats / coverage per gallon. With the 350 sq ft/gal default and two coats, divide paintable area by 175.
- Recommended paint = raw paint x (1 + buffer). The default 10% buffer covers touch-ups, mistakes, and dye-lot insurance.
- Buy quantity = recommended paint rounded up to the next quarter-gallon equivalent (one gallon = four quarts).
Real-world coverage rates by surface
Manufacturer baselines are based on smooth primed drywall. Adjust for your actual surface.
| Surface type | Realistic coverage | Notes |
|---|---|---|
| Smooth primed drywall | 350 sq ft / gal | Manufacturer baseline |
| Orange peel texture | 270-300 sq ft / gal | Mild texture, slight drop |
| Knockdown texture | 260-290 sq ft / gal | Common in residential |
| Popcorn ceiling | 200-230 sq ft / gal | Use a thick nap roller |
| Bare/new drywall | 180-230 sq ft / gal first coat | Primer strongly recommended |
| Stucco / brick (interior) | 150-200 sq ft / gal | Use a masonry-rated product |
Worked examples by room size
Four common interior paint projects, broken down step by step.
| Project | Dimensions | Paintable area | Raw paint | With buffer | Buy |
|---|---|---|---|---|---|
| Standard bedroom | 12 x 14 ft, 8 ft ceilings, 2 coats, walls only | 376 sq ft | 2.15 gal | 2.36 gal | 2.5 gal (1 gal + 1.5 qt or 1 gal + 1 qt rounded up) |
| Bedroom + ceiling | 12 x 14 ft, 8 ft ceilings, 2 coats walls + 1 coat ceiling | 376 sq ft walls + 168 sq ft ceiling | 2.15 gal walls + 0.48 gal ceiling | 2.89 gal total | 3 gal |
| Small bathroom | 8 x 6 ft, 8 ft ceilings, 2 coats | 180 sq ft (subtract door + small window) | 1.03 gal | 1.13 gal | 1.25 gal (1 gal + 1 qt) |
| Large living room | 20 x 16 ft, 9 ft ceilings, 2 coats | 648 sq ft (subtract 2 doors + 3 windows) | 3.7 gal | 4.07 gal | 4 gal (one 2-gallon + one 2-gallon, or one 5-gal) |
Standard bedroom. Most common project size. One gallon plus one quart usually works; round up if walls are textured.
Bedroom + ceiling. Use the same paint for walls and ceiling, or buy a separate ceiling paint in 1-gallon size.
Small bathroom. Bathrooms need mildew-resistant paint. The extra quart handles tight corners and trim around fixtures.
Large living room. Above 4 gallons, the 5-gallon pail is usually cheaper per gallon. Excess works for touch-ups for years.
One gallon, two gallons, or a 5-gallon pail?
Which size of paint to buy depends on total gallons, not just dollars per gallon.
Under 1.5 gallons: buy one gallon plus quarts. The quart format lets you fine-tune the order without committing to a second full gallon you may not use.
1.5 to 3 gallons: buy two single gallons. Two 1-gallon cans give you flexibility for sample testing on the wall and easier portability. Cost per gallon is usually similar to the 2-gallon pack.
3 to 4.5 gallons: two 2-gallon pails (or one 2-gallon plus singles). Higher per-gallon prices than the 5-gal but no waste if you only need 3.5 gallons.
4.5 gallons or more: the 5-gallon pail is usually 15-25% cheaper per gallon than smaller sizes. Excess paint is fine for touch-ups for 2+ years if sealed properly.
Common mistakes that cause paint shortages
Five errors that send DIY painters back to the store mid-project.
If you need primer first, you have THREE coats of product going on, not two. Either buy enough primer separately or use a primer+paint combo that explicitly covers your contrast level.
Two standard doors and three windows can be 80-100 sq ft of non-paintable area. On a small bedroom that is a full quart of over-ordered paint.
Running out 80% through is the worst case. The new batch may not match perfectly (dye lot variation), and store runs eat the time you saved. Round up generously - leftover paint is cheap insurance.
Adding a ceiling coat is roughly 0.5 gallons for a typical bedroom. Plan it explicitly or you will be a quart short.
Frequently asked questions
The questions DIY painters ask most often before buying.
How much paint do I need for a 12 x 14 room with 8 ft ceilings?
A 12 x 14 room with 8 ft ceilings has 416 square feet of wall area (2 x (12 + 14) x 8). Subtract about 40 square feet for one standard door and two windows, leaving ~376 sq ft of paintable surface. At the default coverage of 350 sq ft per gallon, two coats need about 2.15 gallons. After a 10% buffer for touch-ups and texture, round up to 2.5 gallons (one gallon plus one quart, or one and a half 2-gallon cans). Add the ceiling (168 sq ft, one coat) and you cross into 3 gallons total.
How many coats of paint should I plan for?
Two coats is the safe default for almost every interior repaint. One coat works only when you are recoating the exact same color over a clean, primed, in-good-shape surface - and even then, the second coat protects coverage uniformity. Three coats are needed when going from a dark color to a light color, when using high-coverage colors like deep reds, or when paint-and-primer-in-one is being asked to do work that real primer should do.
What does 350 square feet per gallon actually mean?
It is the manufacturer's stated coverage rate per gallon per coat under ideal conditions: smooth, primed drywall, applied with a standard 3/8 inch nap roller. Real-world coverage drops with textured walls (knockdown, popcorn ceilings drop to 200-250 sq ft/gal), porous surfaces, and dark-to-light color changes. Always check the spread rate on the paint can - some premium paints advertise 400 sq ft/gal, while cheaper paints can drop to 250.
Do I subtract doors and windows from the wall area?
Yes, for any opening larger than about 15 square feet. A standard interior door is roughly 20 sq ft, and a typical window is 12-15 sq ft. Subtracting them prevents a 15-20% over-order on rooms with multiple openings. The calculator takes one combined openings number to keep the input simple - just add up the rough areas.
How do I estimate paint for ceilings?
Ceiling area is simply room length x room width. Most ceilings only need one coat if you stick with white-on-white. Use ceiling-specific paint (flatter sheen, splatter-resistant formula) and budget the same coverage rate as walls. A 10 x 12 ceiling needs about 0.34 gallons for one coat - round up to one quart or share with another room.
Why does paint come in gallons but the calculator suggests quarter-gallon amounts?
Paint is sold in gallons (or 1-, 2-, and 5-gallon cans) and quarts. The calculator rounds to the next quarter-gallon equivalent so you can decide whether to buy one gallon, one gallon plus a quart, or jump to two gallons. Rounding down to the wrong increment is the most common reason DIY painters run out one wall before finishing.
Should I use primer separately, or paint-and-primer-in-one?
Use a dedicated primer when you are covering stains, going dark-to-light, painting over glossy surfaces, or working on new drywall. Paint-and-primer-in-one products are designed for the easy case: same-color recoating or low-contrast changes on already-painted, in-good-shape walls. Primer adds a coat to your math - factor it into the gallon estimate.
How long does a gallon of leftover paint stay good?
Properly sealed, an unopened gallon of latex paint stays usable for 2-10 years. Once opened, expect 1-2 years if you wipe the rim clean, seal the lid tight, and store it cool (above freezing, below 80 degrees F). Label the can with the room and date - you will want it for touch-ups within the first 6 months when colors still match the surrounding paint.
Related calculators and guides
Pages that pair with the paint estimate.
Paint coverage per gallon guide How spread rates vary by surface type, sheen, and color contrast. Imperial / metric conversion guide Convert square feet to square meters and gallons to liters cleanly. Flooring calculator Pair the paint estimate with the flooring order for the same room. How these estimates work Rounding, buffer, and unit conversion rules across the site.