Paint Calculator
Estimate gallons of interior or exterior paint from room dimensions or direct wall area. Deducts doors and windows and applies coats and waste.
Quick answers
How many square feet does a gallon of paint cover?
One gallon covers about 350 ft² in a single coat on smooth, primed drywall. That is the spread rate this calculator uses by default. Two coats halve it to roughly 175 ft² of finished wall per gallon, and rough or porous surfaces cut it further, so the container count depends as much on substrate and coat count as on room size.
Coverage by container size at 350 ft² per gallon
| Container | One coat | Two coats |
|---|---|---|
| 1 pint (0.125 gal) | 43.8 ft² | 21.9 ft² |
| 1 quart (0.25 gal) | 87.5 ft² | 43.8 ft² |
| 1 gallon | 350 ft² | 175 ft² |
| 2 gallons | 700 ft² | 350 ft² |
| 5 gallons | 1,750 ft² | 875 ft² |
Figures assume no waste allowance. Enter a different spread rate above to recompute for your product and substrate.
How many square feet does 5 gallons of paint cover?
5 gallons covers about 1,750 ft² in one coat, or 875 ft² in two coats, at 350 ft² per gallon. A 5-gallon pail is therefore roughly the right amount for two coats on the walls of a 1,000 ft² single-storey home interior, before deducting openings.
How much will a quart or a pint of paint cover?
A quart covers about 87.5 ft² and a pint about 43.8 ft², one coat. Both are trim-and-touch-up quantities rather than wall quantities: a quart is roughly one interior door and its casing, and a pint suits a windowsill, a shelf, or colour sampling.
How much paint do I need per square foot?
Divide by the spread rate: one square foot needs about 0.0029 gallons per coat at 350 ft² per gallon. Practically, plan one gallon per 350 ft² per coat and round up to the next container, because paint is sold in fixed sizes and a partial gallon still costs a full one.
Typical published spread rates by substrate
| Surface | Spread rate per gallon | Why it differs |
|---|---|---|
| Smooth, primed drywall | 350-400 ft² | Calculator default; least absorbent |
| Textured or orange-peel drywall | 300-350 ft² | Texture adds real surface area |
| Wood siding, exterior | 250 ft² | Grain and end-grain absorb more |
| Primer, any surface | 200-300 ft² | Formulated to soak in, not cover |
| Stucco, brick, masonry | 175-200 ft² | Highly porous and deeply profiled |
Manufacturer figures on the label assume ideal conditions. The label rate is where you start, not where you finish.
Assumptions
- Default coverage is 350 ft² per gallon per coat (≈32.5 m²/gal) for quality latex on smooth surfaces.
- Default door deduction is 21 ft² (≈1.95 m²); window deduction is 15 ft² (≈1.39 m²) each.
- Two coats are assumed unless you change the setting.
- Does not include ceiling area unless included in wall area entry.
- Primer is calculated separately if coverage differs.
Paintable area = wall area − openings (all converted to m² internally). Gallons = (paintable area × coats ÷ coverage rate) × (1 + waste%). Results round up to the nearest quarter gallon. Coverage and openings use the area units you select (ft² or m²).12 × 10 ft room, 8 ft ceilings, 2 coats
- Perimeter = 2×(12+10) = 44 ft. Wall area = 44 × 8 = 352 ft². Minus 1 door (21) and 2 windows (30) = 301 ft² paintable. Two coats on 350 ft²/gal: (301×2)÷350 = 1.72 gal → 1.75 gal with quarter-gallon rounding, plus waste. Metric equivalent: enter lengths in m and openings/coverage in m² for the same physical result.
How much paint do I need for a room?
Paint is bought against wall surface area, never floor area. Start with the perimeter: for a rectangular room that is 2 × (length + width). Multiply the perimeter by the ceiling height to get gross wall area, then subtract the openings. This calculator deducts 21 ft² for each standard door and 15 ft² for each standard window by default, and it lets you enter custom opening areas in ft² or m² for patio doors and picture windows. Gallons then equal paintable area × number of coats divided by the coverage rate, multiplied by one plus your waste percentage, with the answer rounded up to the nearest quarter gallon because retail paint is sold in quart increments.
Two settings decide almost everything. The first is coats: the default is two, and both Sherwin-Williams and Benjamin Moore recommend two coats on bare substrates for full color development and performance [1][2]. The second is the spread rate. The default of 350 ft² per gallon is the conservative end of a published range, and it assumes a smooth, primed, uniformly porous surface. The calculator does not include ceilings unless you add that area yourself, and it does not include primer, which should be figured as its own coat at its own coverage rate. Everything here is a planning estimate; the can label always governs.
How many square feet does a gallon of paint cover?
Manufacturer data sheets publish a spread rate tied to a specific wet film thickness. Sherwin-Williams ProMar 200 Zero V.O.C. Interior Latex Flat lists coverage of 350 to 400 ft² per gallon at 4 mils wet and 1.4 mils dry [1]. The matching ProMar 200 Zero V.O.C. primer lists 350 to 400 ft² per gallon at 4 mils wet and 1.0 mil dry [1]. Benjamin Moore Regal Select Semi-Gloss N551 publishes a higher spread rate of 400 to 450 ft² per gallon at a recommended 3.6 to 4.0 mils wet and 1.3 to 1.5 mils dry [2]. Those are per coat, not per project.
Real walls usually deliver less. Benjamin Moore states plainly that spread rate depends on surface texture and porosity [2], and heavy texture, knockdown, sand finishes, bare masonry, and unprimed joint compound all absorb more material. For planning purposes many painters drop textured interior walls to 250 to 300 ft² per gallon. Application method matters as well: spraying deposits more material and generates overspray losses, while a 3/4 in nap roller cover carries more paint onto a rough surface than a 3/8 in cover. If you switch the coverage field to m² per gallon, remember that 350 ft² per gallon is about 32.5 m² per gallon.
How much paint do I need for a 12x10 room with 8 foot ceilings?
Run it step by step. Perimeter is 2 × (12 + 10) = 44 ft. Gross wall area is 44 × 8 = 352 ft². Deduct one standard door at 21 ft² and two standard windows at 15 ft² each, which is 51 ft² of openings, leaving 301 ft² paintable. Two coats at 350 ft² per gallon is 301 × 2 divided by 350, or 1.72 gallons. Rounded up to the nearest quarter gallon that is 1.75 gallons, and adding a 5 percent allowance pushes it to 1.81, which still rounds to 2 gallons purchased. The named result is one gallon plus three quarts.
Now add the pieces the wall calculation leaves out. The ceiling is 12 × 10 = 120 ft², and two coats of ceiling paint at 350 ft² per gallon is 0.69 gallons, so one gallon. Primer on new drywall is a separate coat: 301 ft² divided by 350 is 0.86 gallons, so one gallon. Trim, doors, and the window casings are usually bought by the quart. The metric route gives the same physical answer: enter dimensions in meters and set both the opening and coverage units to m², and 28.0 m² of paintable wall at 32.5 m² per gallon over two coats is the same 1.72 gallons.
Do I need one coat or two coats of paint?
Plan on two. Sherwin-Williams specifies one coat of ProMar 200 Zero V.O.C. primer followed by two coats of finish over drywall, and notes that priming plus two coats at the recommended film thickness helps where hiding a previous coating or painting new drywall is a factor [1]. Benjamin Moore says that although the quality of its products sometimes makes one-coat coverage achievable, two coats are recommended to achieve full color development and optimize performance, and two coats are recommended on bare substrates [2]. Colour changes make this decisive: going from a saturated red to off-white in one coat is not realistic.
Coats multiply gallons linearly, so the setting matters more than most people expect. On the 301 ft² room above, one coat is 0.86 gallons, two coats is 1.72, and three coats is 2.58. Sherwin-Williams also notes that where repainting involves a drastic color change, a coat of primer improves the hiding performance of the topcoat [1], which is usually cheaper than a third finish coat. Recoat windows matter too: ProMar 200 Flat lists a 4 hour recoat time and Regal Select lists 3 hours, both temperature and humidity dependent [1][2], so a two-coat room is realistically a full day.
How much primer do I need on new drywall?
Treat primer as its own coat with its own coverage rate. The Sherwin-Williams drywall specification is one coat of ProMar 200 Zero V.O.C. Latex Primer plus two coats of finish, and the primer is published at 350 to 400 ft² per gallon [1]. On 301 ft² of paintable wall that is 0.86 gallons, so one gallon. Primer is not optional on new board: Gypsum Association finishing guidance recommends that the painting specification include a priming material applied over the entire prepared gypsum panel surface before decoration, because the primer equalizes the difference in porosity between face paper and joint compound.
Skipping it produces joint photographing, the shadowing of finished joints through the decoration. Sherwin-Williams also lists specific primers for other substrates, such as a block filler on concrete block and a masonry primer on plaster or masonry that has cured about 30 days [1]. Benjamin Moore markets Regal Select as self-priming on properly prepared drywall, cured plaster, and smooth concrete, while still recommending two coats on bare substrates [2]. Read the specification for your product rather than assuming. This calculator sizes one product at one coverage rate at a time, so run primer as a separate calculation.
How to measure
Measure room length and width along the floor. Measure ceiling height at a corner. Count doors and standard windows, or enter custom opening areas with matching ft² or m² units for large patio doors or picture windows.
How many square feet does a gallon of paint cover?
| Product or surface | Published spread rate | Film thickness | Area covered by 1 gallon in 2 coats |
|---|---|---|---|
| Sherwin-Williams ProMar 200 Zero V.O.C. Interior Latex Flat | 350 to 400 ft² per gallon | 4 mils wet, 1.4 mils dry | 175 to 200 ft² |
| Sherwin-Williams ProMar 200 Zero V.O.C. Latex Primer | 350 to 400 ft² per gallon | 4 mils wet, 1.0 mil dry | one coat only, 350 to 400 ft² |
| Benjamin Moore Regal Select Semi-Gloss N551 | 400 to 450 ft² per gallon | 3.6 to 4.0 mils wet, 1.3 to 1.5 mils dry | 200 to 225 ft² |
| Calculator default for smooth primed walls | 350 ft² per gallon | not specified | 175 ft² |
| Textured or porous walls, planning figure | 250 to 300 ft² per gallon | not specified | 125 to 150 ft² |
Published rates assume smooth, primed, uniformly porous surfaces. 350 ft² per gallon is about 32.5 m² per gallon.
How much paint does each room size need for two coats?
| Room with 8 ft ceilings | Gross wall area | After 1 door and 2 windows | Gallons at 350 ft² per gallon | Purchase to nearest quarter gallon |
|---|---|---|---|---|
| 10 ft × 10 ft | 320 ft² | 269 ft² | 1.54 | 1.75 gal |
| 12 ft × 10 ft | 352 ft² | 301 ft² | 1.72 | 1.75 gal |
| 12 ft × 12 ft | 384 ft² | 333 ft² | 1.90 | 2.00 gal |
| 14 ft × 12 ft | 416 ft² | 365 ft² | 2.09 | 2.25 gal |
| 16 ft × 14 ft | 480 ft² | 429 ft² | 2.45 | 2.50 gal |
| 20 ft × 16 ft | 576 ft² | 525 ft² | 3.00 | 3.00 gal |
Openings deducted are 21 ft² for the door and 15 ft² each for two windows, a total of 51 ft². Ceilings not included.
How much do doors and windows reduce paintable area?
| Opening | Area deducted | Paint saved on 2 coats at 350 ft² per gallon | How to enter it |
|---|---|---|---|
| Standard interior door, about 3 ft × 7 ft | 21 ft² | 0.12 gal | Calculator default per door |
| Standard window, about 3 ft × 5 ft | 15 ft² | 0.09 gal | Calculator default per window |
| Picture window, 6 ft × 5 ft | 30 ft² | 0.17 gal | Custom opening area |
| Sliding patio door, 5 ft × 8 ft | 40 ft² | 0.23 gal | Custom opening area |
| Garage door opening, 16 ft × 7 ft | 112 ft² | 0.64 gal | Custom opening area |
Deduct openings, not trim. Casings, jambs, and doors themselves are usually bought separately by the quart.
Common mistakes
- Using floor square footage instead of wall surface area.
- Forgetting the second coat on new drywall or bold color changes.
- Using manufacturer best-case coverage on textured or porous walls.
- Entering metric opening areas while leaving the unit on ft² (or the reverse).
Frequently asked questions
How many gallons of paint do I need for a 12x12 room?
How much paint do I need for 1000 square feet of wall?
How many square feet does a gallon of paint cover?
Do I need to prime new drywall before painting?
How much paint do I need for a ceiling?
Why does my paint cover less than the label says?
How many coats of paint do I need over a dark color?
Sources and references
Last updated:
- ProMar 200 Zero V.O.C. Interior Latex Flat B30 Series product data sheet: coverage 350 to 400 sq ft per gallon — The Sherwin-Williams Company (2023)
- Regal Select Premium Interior Paint and Primer Semi-Gloss N551 technical data sheet: spread rate 400 to 450 sq ft per gallon — Benjamin Moore and Co. (2025)
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