Paint Coverage Calculator
Calculate how many gallons of paint to buy for a room. Enter dimensions or wall area, deduct doors and windows, plan for two coats, and add ceiling and primer.
Figure out exactly how much paint to buy. Enter your room's size — the tool subtracts doors and windows and plans for two coats — or type a wall area you already know. Add the ceiling or primer if you need them.
How to measure
Enter the room's dimensions and let the tool figure the wall area, or type a wall area you already know.
Room size
Length, width, and ceiling height in feet.
Doors & windows
The tool deducts about 21 sq ft per door and 15 sq ft per window from the wall area.
≈ 365 sq ft of wall (deducted 51 sq ft for doors & windows)
Wall texture
Smooth drywall spreads paint the farthest; textured and especially heavily textured surfaces (knockdown, popcorn) soak up more.
Number of coats
Most jobs need two coats for even color and full coverage — especially over a different color or new drywall.
Paint to Buy
2 gallons
for 365 sq ft over 2 coats
Plan for two coats
Most jobs need two coats for even color and full hide — especially over a different color or fresh drywall — and this estimate already reflects the coats you chose. It's still smart to keep a little extra for touch-ups; a sealed can stores for months, and re-buying later risks a slight batch color difference.
Estimates use a typical 375 sq ft per gallon on smooth walls (less for textured), 300 for primer, and deduct about 21 sq ft per door and 15 per window. They cover walls (and the ceiling if selected) but not trim, doors, closets, or accent walls in a second color — estimate those separately. Dark-over-light or vivid colors sometimes need an extra coat. Always check your specific product's stated coverage.
💡About this calculator▼
"How much paint do I need?" is the question every project starts with — and getting it wrong costs you either a second trip to the store mid-coat or a shelf of half-used cans. This calculator gives you a confident gallon count before you buy.
Enter your room's length, width, and ceiling height and the tool works out the wall area and subtracts your doors and windows automatically — or, if you already know your wall area, just type it in. Set the wall texture and number of coats, and optionally add the ceiling and a primer estimate. You get the number of gallons to buy, rounded up to whole cans.
Two things trip people up, and this tool handles both: most rooms need two coats (not one) for even, full-hide color, and primer is a separate product many people forget to buy for new drywall, patches, or a big color change. Plan for them up front and you'll finish the job with one shopping trip.
The calculator finds your paintable area, divides by a realistic coverage rate, multiplies by your coats, and rounds up to whole gallons.
In dimensions mode, it calculates wall area as the room's perimeter times the ceiling height — that's 2 × (length + width) × height — then subtracts your openings, counting about 21 square feet per door and 15 per window. That net figure is your wall area. If you switch to area mode, it simply uses the square footage you enter. Turn on the ceiling option and it adds the ceiling (length × width) to the total.
Next it sets a coverage rate. A gallon of wall paint covers roughly 375 square feet of smooth drywall in one coat. The tool derates that for texture: lightly textured walls (orange-peel, knockdown) and heavily textured surfaces (popcorn, rough plaster) have more hidden surface area and drink more paint, so the effective coverage drops.
Then it multiplies your paintable area by the number of coats, divides by the effective coverage, and rounds up — you buy whole gallons, not fractions. If you include primer, it's estimated separately at one coat and about 300 square feet per gallon, because primer is its own product. The exact formula and a worked example are below.
📐How it's calculated▼
The estimate builds your paintable area, derates coverage for texture, and rounds up.
Step 1 — Wall area: From dimensions: Wall area = 2 × (Length + Width) × Ceiling height − openings Openings = (Doors × 21 sq ft) + (Windows × 15 sq ft) From area mode: Wall area = your entered value
Step 2 — Paintable area: Paintable area = Wall area + Ceiling (Length × Width, if included)
Step 3 — Effective coverage: Effective coverage = 375 × Texture factor (smooth 1.0, textured 0.85, heavy 0.7)
Step 4 — Gallons: Paint = (Paintable area × Coats) ÷ Effective coverage, rounded up Primer (if included) = Paintable area ÷ (300 × Texture factor), rounded up
Example: A 12 × 14 ft room, 8 ft ceilings, 1 door, 2 windows, smooth walls, 2 coats
→ Gross wall: 2 × (12 + 14) × 8 = 416 sq ft
→ Openings: (1 × 21) + (2 × 15) = 51 sq ft
→ Wall area: 416 − 51 = 365 sq ft
→ Paint: (365 × 2) ÷ 375 = 1.9 gal → buy 2 gallons
Add the ceiling and the paintable area jumps to 533 sq ft, pushing you to 3 gallons — a good reminder to decide on the ceiling before you shop.
📎Source: U.S. Environmental Protection Agency — Lead-Safe and Painting Guidance
🔍Finding your inputs▼
How to measure: Use room dimensions if you know the length, width, and ceiling height — it's the easiest path and lets the tool deduct doors and windows for you. Switch to known wall area if you've already measured an irregular space, or you're painting just a few specific walls and have the square footage.
Room length, width, and ceiling height: In feet. Most ceilings are 8 feet; many newer or higher-end homes run 9 or 10. For an open or L-shaped space, you can run the calculator once per rectangular section and add the gallons, or switch to area mode with your total wall square footage.
Doors and windows: The count of each in the room. The tool removes about 21 square feet per door and 15 per window from the wall area, since you won't paint those. If your windows are unusually large (picture windows, sliders), it's fine to count one big window as two. Skipping this step is why people over-buy.
Wall area (area mode only): Your total paintable wall square footage, already net of doors and windows. Use this when you've measured directly or have an odd-shaped room the dimension fields can't capture.
Wall texture: How smooth the surface is. Smooth flat drywall covers best. Textured walls — orange-peel or knockdown — have more surface area and use more paint. Heavy texture, like popcorn ceilings or rough plaster, uses the most. Match this honestly; it meaningfully changes how far each gallon goes.
Number of coats: Two is standard and usually the right choice — one coat rarely gives even, full-hide color, especially over a different color or new drywall. Choose one coat only for a light refresh in the same color, or three for dramatic color changes or going light over dark.
Include ceiling / Include primer: Turn on the ceiling to add it to the estimate (it's the room's footprint, length × width). Turn on primer to get a separate primer quantity — worth it over bare drywall, patched or repaired areas, water or smoke stains, or a big color change, since primer helps your color coats cover evenly.
⚠️Special situations▼
I'm painting over a dark or very different color
Big color changes — especially light over dark, or a vivid color — often need an extra coat or a tinted primer to fully hide what's underneath. Bump the coat count to three, or turn on primer (ask the paint counter to tint it toward your topcoat), which can save you a third finish coat. Reds, deep blues, and bright yellows are notorious for needing extra coats no matter how good the paint, so budget a little more for those.
My room is open-plan or an odd shape
The dimension fields assume a rectangular room. For an L-shaped or open-plan space, split it into rectangles, run the calculator on each, and add the gallons — or measure the actual wall lengths, multiply by ceiling height, subtract openings, and enter that total in area mode. Don't forget partial walls, knee walls, and the sides of bump-outs or nooks; they add up in irregular spaces.
Do I really need primer?
Not always. You can usually skip dedicated primer when repainting a similar color over a sound, previously painted wall — a quality paint-and-primer-in-one is fine there. Reach for primer over bare or new drywall (it's very absorbent), over patches and joint compound, over water or smoke stains (use a stain-blocking primer), over glossy surfaces, and for major color changes. When in doubt on new or repaired walls, one coat of primer makes the color coats go on more evenly and often saves paint overall.
I'm also doing the trim, doors, and ceiling
This estimate covers walls (and the ceiling if you toggle it on), but trim and doors are usually a different product and sheen — semi-gloss or satin enamel — so buy them separately. As a rough guide, a gallon of trim paint covers the doors and baseboards of an average room or two. The ceiling, if you include it here, is added as the room's footprint (length × width); flat ceiling paint is often its own can too, so plan for three separate products on a full room refresh: walls, ceiling, and trim.
I have leftover paint from before
Unopened or well-sealed paint that hasn't frozen often lasts a couple of years and can be remixed if it's just settled. Subtract any usable leftover from the gallons-to-buy figure. The catch is color matching: even the same color and brand can vary slightly between batches, so use older paint for closets or touch-ups rather than a main wall, or buy all your gallons new from the same batch and have them boxed (combined) at the store for perfect consistency.
❓Common questions▼
How much paint do I need for a room?
It depends on the wall area, the number of coats, and the wall texture. As a rule of thumb, an average 12 × 14 ft room with 8-foot ceilings needs about 2 gallons for two coats of walls, plus another gallon or so if you're doing the ceiling. A gallon of paint covers roughly 350–400 square feet of smooth wall per coat. Enter your room's size above for a number tailored to your space, with doors and windows deducted.
How many square feet does a gallon of paint cover?
A gallon of quality wall paint covers about 350 to 400 square feet in one coat on smooth drywall — this calculator uses 375 as a realistic middle. Coverage drops on textured surfaces (orange-peel, knockdown) and drops more on heavy texture like popcorn ceilings, which have far more surface area. Porous bare drywall also takes more, which is part of why primer helps. Always check your specific product's stated coverage, since it varies by paint quality and color.
Should I use one coat or two?
Two coats is the standard for a reason: one coat rarely delivers even color and full coverage, especially over a different color, a patch, or new drywall, and you'll often see roller streaks or the old color ghosting through. Use a single coat only for a light freshening in the same color over a sound wall. Going light over dark or using a vivid color can even need three. This calculator defaults to two and lets you adjust.
Do I need primer before painting?
Sometimes. Prime bare or new drywall (it soaks up paint unevenly otherwise), patched and repaired spots, water or smoke stains (with a stain-blocking primer), glossy surfaces, and big color changes. You can usually skip a separate primer when repainting a similar color over a sound, previously painted wall, where a paint-and-primer-in-one works well. Toggle primer on in the calculator to see how much you'd need; it's a separate product from your color coats.
Should I subtract doors and windows when estimating paint?
Yes, for a more accurate number — though erring slightly high is no disaster. This calculator deducts about 21 square feet per door and 15 per window automatically in dimensions mode. For a room with a couple of doors and several windows, that's often 80–120 square feet you're not painting, which can be the difference of a quart or a gallon. If your windows are very large, count them as more than one to keep the estimate honest.