Interior Paint Calculator
Stop guessing how many cans of paint to buy. Enter your wall area, number of coats, and sheen, and this calculator tells you exactly how many gallons and cans you need, plus the total cost.
Prefilled from the selected product — adjust to match your can label or surface porosity.
Covers spills, absorption, and touch-ups. 10–15% is normal.
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Application tips
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Coverage & coats
Product profile
Paint coverage is based on square footage, not room dimensions alone. Multiply the area you’re painting by the number of coats you’re applying, add a waste percentage for rolling loss and touch-ups, then divide by the coverage rate on the can (in square feet per gallon, which varies by sheen). Round up to the nearest whole can to get your final purchase count.
Interior Paint Coverage by Sheen
Coverage per gallon drops slightly as sheen increases because glossier finishes carry more resin and less pigment volume.
| Sheen | Coverage per Gallon | Best For |
|---|---|---|
| Flat/matte | 400 sq ft | Ceilings and low-traffic walls |
| Eggshell | 375 sq ft | Living rooms, bedrooms |
| Satin | 350 sq ft | Kitchens, bathrooms, trim-adjacent walls |
How to Calculate Interior Paint Gallons
- Measure the length and height of each wall, or use total linear wall footage times ceiling height.
- Subtract large openings like sliding doors or big windows if they take up significant wall area.
- Multiply the area by the number of coats you plan to apply.
- Add a waste percentage, typically 5%, for roller loss and touch-ups.
- Divide by your paint’s coverage rate to get gallons, then round up to whole cans.
Worked example
For 40 ft of wall at 8 ft ceilings (320 sq ft), 2 coats of eggshell:
- Wall area40 x 8 ft = 320 sq ft
- Coats2
- Paint sheenEggshell (375 sq ft/gal)
- Waste factor5%
- Total gallons needed1.79 gal
- Cans to buy2 (1-gal cans)
- Estimated cost$64 (2 x $32)
Accounting for Doors, Windows, and Primer
This calculator works off the total area you enter. For a typical room, standard doors take up about 20 sq ft and standard windows about 15 sq ft — subtract those from your total wall area before entering it if you have several large openings, or skip the deduction if you’d rather have a little cushion built in. Small deductions rarely change your can count since paint rounds up to whole cans anyway.
If you’re painting over a dark color, bare drywall, or repaired patches, add a coat of primer first and calculate it separately. Primer coverage runs close to the same as flat paint, but it’s a different product and a different can count than your finish coats.
Common mistakes
- Not subtracting doors and windowson a room with several openings, which overestimates how much paint you need.
- Only budgeting one coatmost color changes and new drywall need two coats for even, opaque coverage.
- Using the wrong sheen for the roomflat shows less texture but doesn’t hold up to scrubbing in kitchens and baths the way satin does.
- Skipping primer on bare or dark wallsprimer isn’t the same product as finish paint and needs its own gallon count.
What this calculator assumes
Adjust your result if your project differs from these.
- Area entered is the total wall square footage being painted
- Coverage rates assume smooth, primed drywall in good condition
- Two coats is the default for full, even color coverage
- Does not separately calculate primer, ceiling paint, or trim paint
- Waste percentage covers roller loss and touch-ups, not a full extra coat
Common questions
How many coats of paint do I need?
Two coats is standard for most color changes and gives the most even, opaque finish. One coat can work for a very close color match over paint in good condition.
Do I need primer too?
Yes if you’re painting bare drywall, a big color change, or repaired patches. Primer coverage is roughly similar to flat paint but calculate it as a separate gallon count.
What's the difference between flat, eggshell, and satin?
Flat hides wall imperfections best and suits ceilings and low-traffic rooms. Eggshell is a popular all-purpose residential finish. Satin has more sheen and holds up better to washing in kitchens and bathrooms.
Should I subtract doors and windows from my area?
It helps for rooms with several large openings, but the calculator rounds up to whole cans anyway, so small deductions often don’t change your final can count.
How much paint is left over from a typical gallon?
It varies with wall texture and technique, but budgeting the calculator’s waste percentage covers normal roller loss and touch-up needs.
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Interior Paint Calculator Estimate
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Project
| Shape | — |
| Dimensions | — |
| Area | — |
| Product | — |
| Coverage | — |
| Coats | — |
| Overage allowance | — |
Shopping list
| Total product | — |
| Cans needed | — |
| Estimated total cost | — |
Notes
Estimate generated by materialcalculate.com. Confirm quantities and coverage with your product label before ordering.