Paint Calculator
Gallons of paint for a room from wall length and height, minus doors and windows, for any number of coats and coverage rate — with ceiling, liters and cost.
Paint Calculator: with the default inputs, gallons to buy is 2.
Use total wall length for a single wall, a hallway, or an odd-shaped room — enter it under More options.
Floor to ceiling. 8 ft is standard; 9 ft in many newer homes.
Not painted; each subtracts about 20 sq ft.
Each subtracts about 15 sq ft.
Two coats is standard; one may do over a similar color, three for dark-to-light or red.
Manufacturers quote 350–400 sq ft per gallon on smooth, primed walls. Use 250–300 on textured or bare drywall.
Rounded up to whole gallons.
- Gallons before rounding
- 1.91
- Liters
- 7.2
- Area to paint (one coat)
- 334 ft²
- Total coverage needed (all coats)
- 668 ft²
- Paint cost
- $0.00
Assumptions
- Openings deducted at 20 ft² per door and 15 ft² per window (industry estimating convention); adjustable under More options.
- Coverage is per coat; the same rate is applied to walls and ceiling.
- Trim, primer and touch-up are not included.
| Surface | Coverage |
|---|---|
| Smooth, previously painted drywall | 350–400 ft² (32–37 m²) |
| New drywall, primer coat | 300–350 ft² |
| Textured or knock-down walls | 250–300 ft² |
| Rough stucco, brick, masonry | 150–250 ft² |
| Spray application (overspray loss) | About 20–30% less than rolling |
Check the can — coverage is printed on the label for that specific product.
| Coverage (ft² per gallon) | Gallons needed | Gallons to buy | Typical of |
|---|---|---|---|
| 150 | 4.45 | 5 | Rough stucco, brick, bare masonry |
| 200 | 3.34 | 4 | Heavy texture, popcorn ceilings |
| 250 | 2.67 | 3 | Knock-down texture, bare drywall |
| 300 | 2.23 | 3 | New drywall over primer |
| 350 | 1.91 | 2 | Smooth previously painted walls |
| 400 | 1.67 | 2 | Smooth walls, premium paint |
You entered 350 ft² per gallon. The spread between the top and bottom rows is more than double — if you are unsure, buy for the pessimistic row and return the unopened can.
How this is worked out
The formula
Wall area = perimeter × height − (doors × 20 ft²) − (windows × 15 ft²) Total area = (wall area + ceiling area) × coats Gallons = total area ÷ coverage per gallon, rounded up Room perimeter = 2 × (length + width)
Open How it’s calculated above to see this worked through with your own numbers.
What you enter
- What are you measuring?
- Use total wall length for a single wall, a hallway, or an odd-shaped room — enter it under More options.A room (four walls from length × width) · Total wall length (More options)
- Room length
- A number.in ft, in, m, cm · 0 or more · defaults to 12
- Room width
- A number.in ft, in, m, cm · 0 or more · defaults to 12
- Wall height
- Floor to ceiling. 8 ft is standard; 9 ft in many newer homes.in ft, in, m, cm · 0 or more · defaults to 8
- Doors
- Not painted; each subtracts about 20 sq ft.from 0 to 100 · whole numbers only · defaults to 1
- Windows
- Each subtracts about 15 sq ft.from 0 to 100 · whole numbers only · defaults to 2
- Coats
- Two coats is standard; one may do over a similar color, three for dark-to-light or red.from 1 to 5 · whole numbers only · defaults to 2
- Include the ceiling
- Turn this on or off.defaults to off
- Coverage per gallon
- Manufacturers quote 350–400 sq ft per gallon on smooth, primed walls. Use 250–300 on textured or bare drywall.in ft², m² · 1 or more · defaults to 350
- Total wall length(under More options)
- Add up the length of every wall you're painting.in ft, in, m, cm · 0 or more · defaults to 48
- Area per door(under More options)
- A 3 × 7 ft door is 21 sq ft; 20 is the usual estimating figure.in ft², m² · 0 or more · defaults to 20
- Area per window(under More options)
- A 3 × 5 ft window is 15 sq ft.in ft², m² · 0 or more · defaults to 15
- Price per gallon(under More options)
- Leave 0 to skip the cost estimate.in dollars · 0 or more · defaults to 0
What you get back
- Gallons to buymain answer
- Rounded up to whole gallons.
- Gallons before rounding
- Liters
- Area to paint (one coat)
- Total coverage needed (all coats)
- Paint cost
What this assumes
- Openings deducted at 20 ft² per door and 15 ft² per window (industry estimating convention); adjustable under More options.
- Coverage is per coat; the same rate is applied to walls and ceiling.
- Trim, primer and touch-up are not included.
About this calculator
Paint is one of the few materials where running out mid-job is worse than buying too much: the second can is never quite the same batch, and the store may not have it. This calculator gives you the real number — wall area minus openings, times coats, divided by the coverage the manufacturer actually prints on the can.
How to use it
For a normal room, leave the mode on A room and enter the length, width and wall height. Count doors and windows (they're subtracted at 20 and 15 sq ft each — adjust those under More options if you have a sliding door or picture window). Set the number of coats and the coverage. Tick Include the ceiling if you're doing it in the same paint; most people buy a separate flat ceiling white, so run it twice.
For a hallway, a single accent wall or a room with a lot of jogs, switch to Total wall length and add up every wall you'll paint.
Coverage is the number that matters
Most premium interior paints claim 350–400 sq ft per gallon. That's on a smooth, sealed, previously painted wall with a ⅜-in nap roller. Reality:
- New drywall and patched areas soak up paint — prime first, or expect 300 sq ft.
- Texture (orange peel, knock-down) has more surface than it looks: figure 250–300.
- Deep colors, especially reds and yellows, hide poorly and may need three coats regardless of the label.
- Spraying wastes 20–30% to overspray but goes on more evenly.
The default of 350 is a realistic middle. If the can says 400 and your walls are in good shape, use 400.
Reading the results
Gallons to buy is rounded up to whole gallons. If the exact figure is, say, 2.2, you'll see a note suggesting two gallons and a quart rather than three gallons. Total coverage needed is the square footage across all coats — handy when comparing a 5-gallon bucket (usually 10–15% cheaper per gallon) against singles.
Trim, doors and baseboards aren't included. A quart of trim enamel covers about 100 linear feet of standard baseboard or 3–4 doors, both sides.
Frequently asked questions
▸How much paint do I need for a 12×12 room?
With 8-ft ceilings, one door and two windows, the walls are about 334 sq ft. Two coats at 350 sq ft per gallon is 1.9 gallons — buy two gallons, or three if you're also doing the ceiling.
▸How many square feet does a gallon of paint cover?
Manufacturers rate most interior paints at 350–400 sq ft per gallon per coat on smooth walls. Textured, porous or unprimed surfaces drop that to 250–300.
▸Do I really need two coats?
Usually. One coat can work when the new color is close to the old one and you're using a premium paint-and-primer product. Going lighter over dark, or using a saturated color, often takes three.
▸Should I subtract windows and doors?
Yes, for large ones. A standard door is about 20 sq ft and a window 15, so a room with a door and two windows loses 50 sq ft — about a seventh of a gallon per coat. Ignore tiny windows.
▸How much paint for a ceiling?
Ceiling area is length × width. A 12 × 12 ceiling is 144 sq ft, so one coat takes under half a gallon; most ceilings need two coats of flat white.
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