Paint Calculator

Paint is bought by area too, like drywall, but the coverage figure itself is a range rather than an exact product spec — a gallon doesn't cover a fixed square footage the way a 4×8 sheet covers exactly 32 square feet, because how far a gallon goes depends on the surface, the color change, and how many coats you're applying. This calculator uses the same room-or-area, ceiling toggle, and openings list as the drywall calculator, then adds coats and an optional primer pass on top, dividing by manufacturer-sourced coverage rates instead of a fixed sheet size. Enter your room's dimensions or a wall area you already have, list any doors and windows to subtract, set your number of coats, and toggle primer on if you need it. The result rounds up to a whole gallon — or to quarts if your job comes in under one, so a small accent wall doesn't get rounded all the way up to a gallon you don't need.

Your room

Doors & windows to subtract

Enter your room dimensions above to see results.

How it's calculated

The calculator starts with the same area math as the drywall calculator: gross area from your room dimensions or a direct entry (plus the ceiling, if you're covering it), minus every opening in your list. That net area is multiplied by your number of coats — two coats means painting the same square footage twice — to get the total area-coats to cover. Paint gallons come from dividing that number by a coverage rate in square feet per gallon; because coverage is a sourced range rather than one fixed number, the calculator shows both a single number to buy (based on a middle display figure) and the fuller range underneath it. Primer, if you toggle it on, is calculated separately from its own coverage rate and applied as a single coat regardless of how many coats of paint you're using, since primer is normally applied once. If the total for either paint or primer comes out under a gallon, the result switches to quarts instead of rounding all the way up to a gallon you don't need.

Worked example

A 14 ft × 12 ft room with an 8 ft ceiling, walls and ceiling both covered, one door (3'0" × 6'8") subtracted: gross area = 2 × (14 + 12) × 8 + (14 × 12) = 416 + 168 = 584 sq ft. The door subtracts 20 sq ft, leaving 564 sq ft net. At 2 coats, that's 564 × 2 = 1,128 sq ft-coats of paint to cover. At 350 sq ft per gallon, that's 1,128 ÷ 350 = 3.22 gallons — rounded up to 4 gallons, or 3–5 gallons across the full 250–400 sq ft/gal range. Primer, toggled on and applied as a single coat over the 564 sq ft net area (not doubled for the two paint coats), needs 564 ÷ 250 = 2.26 gallons at the display rate — rounded up to 3 gallons, or 2–3 gallons across the 200–300 sq ft/gal range.

Coats, coverage, and primer

Published coverage figures — 250 to 400 square feet per gallon, depending on the manufacturer — describe a best-case surface: smooth, primed, and not changing color dramatically. Real walls rarely match that exactly. A porous or previously unpainted surface soaks up more paint before it's covered; a textured or heavily patched wall has more actual surface area per square foot of flat wall than a smooth one; and a dramatic color change — a dark wall going light, or the reverse — often needs extra paint to fully hide what's underneath, regardless of what the can's coverage figure says. That's why coverage is shown here as a range rather than a single number, and why buying a little over the calculated amount is cheaper than a second trip to the store mid-project. Two coats is the default here because it's standard practice, not a code requirement or a manufacturer minimum — a single coat rarely hides a color change evenly or wears as well over time, and most professional painters apply two coats as a matter of course rather than gambling on one holding up. Set the coat count to whatever your project actually needs; nothing here treats two as mandatory. Primer is worth buying when you're covering a dramatic color change, painting bare drywall or wood for the first time, covering a stain or repair, or switching between very different paint types (oil to latex, for example) — in those cases it creates a more even, opaque base that the topcoat covers more reliably, often with fewer coats than trying to hide everything with paint alone. Repainting a wall a similar color in reasonable condition is the case where primer is most often skippable, and that's a real time and cost saver, not a corner cut.

Where the coverage figures come from

Paint

BEHR states one gallon of any BEHR paint covers 250 to 400 square feet with one coat — porous, rough, textured, or previously unpainted surfaces need more, as does a dramatic color change; the same figure repeats on their interior and ceiling paint pages. Sherwin-Williams states a gallon typically covers about 350 to 400 square feet. The two disagree on the low end, so the published range here (250–400 sq ft/gal) is the union of both rather than picking one. The spread reflects surface texture, porosity, and how much the color is changing: smooth, primed drywall in a similar color hits the high end, while textured or unprimed surfaces going dark-to-light hit the low end. We use 350 sq ft/gal as the display figure, drawn from:

Primer

Sherwin-Williams states a gallon of primer covers about 200 to 300 square feet. This figure is currently single-sourced — BEHR's published coverage guidance covers paint but not primer at the same level of detail — so it doesn't yet meet this site's usual two-source minimum. Treat it as a starting point and confirm with your primer's own label, especially for a large job. We use 250 sq ft/gal as the display figure, drawn from:

Common mistakes

  • Assuming the coverage number on the can is what you'll actually get. It's a best-case figure for a smooth, primed, minimally-changing-color surface — textured walls, unprimed drywall, and dark-to-light repaints all use more paint per gallon than the label suggests.
  • Buying for one coat when the project needs two. Most interior repaints need two coats for even color and durability — check the can's own recommendation and plan for two unless you have a specific reason not to.
  • Skipping primer on a surface that needs it — bare drywall, a major color change, or a stain or repair patch — and then needing an extra coat or two of the more expensive topcoat to compensate.
  • Rounding a small job up to a full gallon by default. A single accent wall or a small bathroom often only needs a quart, and buying a gallon for a quart-sized job is unnecessary cost and leftover paint.
  • Doubling primer the same way you might double paint. Primer is normally one coat regardless of how many topcoat passes follow it.

FAQ

How much paint do I need for a room?
For a 10 ft × 10 ft room with an 8 ft ceiling, walls only, at two coats: gross area = 2 × (10 + 10) × 8 = 320 sq ft, × 2 coats = 640 sq ft-coats. At 350 sq ft per gallon, that's about 1.83 gallons — rounded up to 2 gallons. Use the calculator above to add your own openings, ceiling, and coat count for the full picture.
Why does my paint coverage seem lower than what the can says?
The can's figure is a best-case number for a smooth, primed surface with a minor color change. Texture, porosity, an unprimed surface, or a dramatic color change all use more paint per gallon than that figure assumes — which is exactly why this calculator shows a range instead of treating the can's number as exact.
How many coats of paint do I need?
Two is standard practice for most interior repaints, not a rule this calculator enforces — it's the default because a single coat rarely hides a color change evenly or wears as well over time. Some jobs need only one coat (a very similar color, a high-quality paint-and-primer product) and some need three (a dramatic color change); set the coat count to what your specific project needs.
Do I need primer?
It's worth it for bare drywall or wood, a major color change, covering a stain or repair patch, or switching between very different paint types. It's often skippable when you're repainting a similar color over a sound existing coat. Primer creates a more even base that the topcoat covers more reliably, sometimes with fewer coats than trying to hide everything with paint alone.
How much paint do I need for a small accent wall?
An 80 sq ft accent wall at two coats is 160 sq ft-coats — well under a gallon at any published coverage rate. At 100 sq ft per quart, that's about 2 quarts, not the full gallon a lot of calculators would round you up to. Enter a small area above to see the quart conversion in action.
Why is primer coverage only backed by one source?
Sherwin-Williams states primer coverage at 200 to 300 square feet per gallon; BEHR's published guidance covers paint coverage but not primer at the same level of detail, so this figure doesn't yet meet the two-source minimum used everywhere else on this site. It's noted here rather than hidden — treat it as a starting point and confirm with your primer's own label for a large job.
Should I buy extra paint for touch-ups?
A little extra is worth keeping. Even the same paint code can vary slightly between production batches, so a held-back partial can from the original job matches a future touch-up better than a fresh gallon mixed later. Round up rather than order exactly to the calculated amount, and store the leftover sealed and labeled.

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