Paint Calculator
The EveryFix Paint Calculator estimates how much paint you need based on your room dimensions, number of doors and windows, and how many coats you plan to apply. Get a quick, reliable estimate in gallons or liters before you head to the store — switch between U.S. Customary and Metric units at the top of the calculator. The deduction for doors and windows uses fixed averages (20 sq ft per door, 15 sq ft per window) rather than your exact opening sizes — accurate for a standard interior door and mid-size window, but it will overstate your paint need if your room has oversized picture windows or French doors, so measure those manually and adjust. Because the number of coats multiplies the entire net wall area rather than adding a flat buffer, going from one coat to two doesn't modestly increase the total — it doubles the paint required, which is why "two coats" estimates run close to double the one-coat figure rather than 20–30% more.
Switch between U.S. Customary and Metric units.
How This Tool Works
Choose U.S. Customary or Metric units, enter the length and width of the room, the wall height, and how many doors and windows it has. Choose how many coats you plan to apply, then get an instant estimate rounded up to the nearest quarter gallon (or half liter).
Formula & Method
We calculate wall area from the room perimeter and height, subtract standard allowances for doors (20 sq ft / 1.86 m²) and windows (15 sq ft / 1.39 m²), multiply by the number of coats, then divide by your paint's coverage rate (default 350 sq ft per gallon, or about 10 m² per liter).
Example Calculation
Take a 14×12 ft room with 9 ft ceilings, 2 doors, and 3 windows, planning 2 coats at the default 350 sq ft/gallon coverage. Perimeter = 2 × (14 + 12) = 52 ft. Gross wall area = 52 × 9 = 468 sq ft. Deductions = (2 doors × 20 sq ft) + (3 windows × 15 sq ft) = 40 + 45 = 85 sq ft. Net wall area = 468 − 85 = 383 sq ft. Total paintable area for 2 coats = 383 × 2 = 766 sq ft. Gallons needed = 766 ÷ 350 = 2.19 gallons (exact: 2.1886). Rounded up to the nearest quarter gallon: buy 2.25 gallons.
Frequently Asked Questions
How much paint do I need for a 12×12 room?+
For a standard 12×12 ft (about 3.7×3.7 m) room with 8 ft ceilings, one door, and two windows, you'll typically need about 2 gallons (roughly 7.5 liters) for two coats. Use the calculator above with your exact dimensions for a precise number.
Can I calculate paint in liters and square meters?+
Yes. Switch the unit toggle to Metric and enter your room in meters — the calculator returns the paint you need in liters, based on a typical coverage of about 10 m² per liter per coat.
Does this account for ceilings?+
No — this calculator estimates wall paint only. If you're painting the ceiling too, calculate its area (length × width) separately and divide by your coverage rate.
Why round up to the nearest quarter gallon?+
Paint stores typically sell in quart and gallon (or half-liter and liter) increments, and running short mid-coat can cause visible touch-up lines, so it's safer to round up.
Does this calculator account for primer?+
No — this estimates finish/topcoat paint only. If you're painting over bare drywall, a dark existing color, or a stain, budget a separate coat of primer (you can run the calculator again with '1 coat' to estimate primer volume separately).
What if my doors or windows are much bigger or smaller than average?+
The calculator deducts a flat 20 sq ft per door and 15 sq ft per window, which matches a standard interior door and a mid-size window. For oversized openings like picture windows or sliding glass doors, measure their actual area and adjust your final estimate manually rather than relying on the fixed deduction.
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