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Calculators

Paint Calculator

This paint calculator answers "how much paint do I need?" the way stores sell the answer. Paint comes by the gallon, but rooms rarely need a round number — enter your room's dimensions once and this calculator nets out doors and windows, applies your number of coats, and turns the result into a real buy list — like "2 gallons + 1 quart" — instead of a single rounded-up guess, priced at three real paint grades so you can see the spread.

Buy list, not a rounded guessPrices editable · reviewed July 2026Texture-aware coverage
416 sqft walls× 2 coats1 door · 2 windows deducted
Coats
Surface (sets coverage)
Heavy covers fresh drywall and knockdown — porous walls drink more paint.
Paint grade & prices — editablereviewed July 2026
BUY LIST371 SQFT × 2
2 gal + 1 qt
2.12 gal needed · rounded to buyable cans
gross walls416 sqft
− doors & windows45 sqft
Paint at your prices$85
Total$85

same cans, economy → premium: $59 – $124

Estimates only, not quotes. Prices are editable national averages — confirm current pricing and quantities with your supplier before you buy.

Plain-English tour

How much paint do I need? How this calculator works

Most paint calculators divide square footage by a coverage number and round up to the next whole gallon — which quietly overbuys by up to a full gallon on an average bedroom. This one shops the way a painter actually would.

First, it finds the paintable area: the four walls combined, minus real allowances for doors (21 sq ft each) and windows (12 sq ft each) rather than ignoring openings. If you're doing the ceiling too, that area is added on separately. Second, it multiplies that area by your number of coats. Third, it divides by your coverage rate, where surface texture matters more than most people expect: a smooth, previously painted wall can approach 400 sq ft/gal, a lightly textured wall behaves more like 300–350, and heavy texture can drop to 250.

Finally, it converts the raw gallons figure into a real buy list: full 5-gallon buckets past about 4.5 gallons, otherwise whole gallons plus a single quart for the leftover — not a whole extra gallon you'll mostly store.

Rolling warm paint onto an interior wall over primer — a paint calculator converts wall area into gallons
Real spread rate over texture is 250–350 sq ft per gallon, not the 400 on the label.
Gallon paint cans, roller tray and painter’s tape on a drop cloth — gallons and primer counted per coat
Openings out, coats in — then round up to whole gallons.
Show the math

The formula

paintable = 2 × (L + W) × H − doors × 21 − windows × 12 (+ L × W ceiling)
gallons = paintable × coats ÷ coverage rate
primer = paintable (1 coat) ÷ 300, whole gallons
buy list = 5-gal buckets ≥ 4.5 gal → gallons → one quart for the tail
cost = cans × your grade's prices · range = economy ↔ premium
With the defaults

Worked example: gallons for a 12×14 room

The calculator's own defaults: a 12 ft × 14 ft bedroom, 8 ft ceilings, one door, two windows, two coats, ceiling not included, and the default 350 sq ft/gal coverage rate.

  1. 1. Wall area2 × (12 + 14) × 8 = 416 sqft gross
  2. 2. Openings(1 × 21) + (2 × 12) = 45 sqft
  3. 3. Paintable416 − 45 = 371 sqft
  4. 4. Two coats371 × 2 = 742 sqft applied
  5. 5. Gallons needed742 ÷ 350 = 2.12 gal
  6. 6. Buy list2 gal + 1 qt (2.25 on hand, ~6% cushion)
  7. 7. Cost, standard grade(2 × $35) + (1 × $15) = $85
  8. 8. Grade spreadeconomy $59 · premium $124 — same cans

That 2.12 doesn't round to "3 gallons" the way a lot of calculators would — two whole gallons cover 2.00, and the remaining 0.12 gallons is 0.48 of a quart, which rounds up to one quart. Same paint job, a $65 spread depending on the line on the shelf.

What we assume

Assumptions & defaults

Paint calculator assumptions
Door / window opening21 sqft · 12 sqft each
Coats2 default (1 for a same-color refresh)
Coverage rate350 sqft/gal default · 250–400 typical
Primer300 sqft/gal, always one coat
Grades (editable)Economy $24 · standard $35 · premium $52 per gal
Buy-list ruleBuckets ≥ 4.5 gal · quart for tails under 1 gal

Coverage is the assumption that matters most here: it's a stand-in for surface texture and porosity, which swing real-world coverage far more than the paint itself does. Prices are editable national-average retail estimates, reviewed July 2026.

Derived from this calculator

Paint coverage by room size, two coats

Gallons of paint by room size at 8 ft ceilings, two coats, 350 sq ft per gallon, openings not deducted
RoomWall square feetBuy (2 coats)
10 × 10 ft3202 gal
12 × 12 ft3842 gal + 1 qt
12 × 16 ft4483 gal
15 × 20 ft5603 gal + 1 qt
20 × 24 ft7044 gal + 1 qt

Straight math at 8 ft ceilings and the label-rated 350 sq ft per gallon, with no doors or windows deducted — your row above will come in slightly lower once openings are netted out. Already know your wall square feet? The "Wall sqft I measured" tab takes the number directly. Paint has no offcut waste — what looks like waste is a coverage-rate problem, explained in the waste factors reference — but fresh drywall drinks primer, and the five-step method behind every estimate here is in how to estimate materials.

Where the numbers come from

Sources & standards

Coverage-rate ranges are cross-checked against the spread-rate figures paint manufacturers publish on their own technical data sheets — major-brand product data sheets each list a per-coat spread rate in the 250–400 sq ft/gallon band depending on sheen and substrate, which is the range this calculator's coverage field defaults to. Door and window opening allowances follow standard residential painting estimating figures. Prices reviewed July 2026 — see how our price reviews work.

Before you roll

Frequently asked questions

Do I really need two coats of paint?
For a color change, over bare drywall, or after any patching, yes — a single coat almost always shows roller lines or the old color through in raking light. If you're refreshing a wall in the same or a very similar color and the existing paint is in good shape, one coat can work: switch Coats to 1 and the calculator halves the topcoat (primer, if you're using it, stays a single coat either way).
Why did the can say 400 sq ft per gallon but this calculator uses 350?
400 sq ft/gal is usually the manufacturer's best-case number — a smooth, previously painted, non-porous wall. Real second-coat coverage on an average lightly textured wall runs closer to 300–350, which is why 350 is the default here. Freshly skim-coated drywall or heavy texture behaves more like 250–300 — use the surface texture selector or edit the coverage field directly.
Should I buy paint-and-primer-in-one instead of a separate primer?
Paint-and-primer-in-one works fine for a same-color refresh over sound existing paint — it's really a thicker paint, not a true primer. For a real color change, especially light over dark or dark over light, a dedicated stain-blocking or bare-drywall primer underneath gets you to full coverage in fewer topcoats. Turn on the primer option here to price that gallon separately.
Do I need an extra coat when painting over a dark color?
Often yes, and sometimes two. Going from a saturated dark color to a much lighter one is the case where the default two topcoats may not fully hide the old color. A tinted primer close to your new shade, or a third topcoat, is the realistic fix — run the calculator with primer on to see that gallon priced out separately before you commit to a can count.
Is ceiling paint different from wall paint?
Ceiling paint is usually a flat sheen formulated to hide texture and application marks without the reflectivity of even a matte wall paint, and it typically runs a little cheaper per gallon. This calculator applies the same coverage rate to ceiling area as to the walls for simplicity — if you're buying dedicated ceiling paint, price that gallon separately using the square footage this tool reports.
How much leftover paint should I keep, and how should I store it?
A single quart is plenty for future touch-ups, and buying the buy list this calculator suggests (rather than rounding up a whole extra gallon) already keeps the leftover small. Store it in a smaller, fully sealed container — paint degrades faster in a half-empty gallon can because of the extra air space — somewhere that won't freeze, and label the lid with color, sheen, and date.
THE WALL BEHIND THE PAINT
Hanging new drywall first? Count the sheets.
Drywall Calculator
Keep estimating

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