What is Paint Calculator?

The Paint Calculator estimates how many gallons or liters of paint you need based on room dimensions. It accounts for doors, windows, and the number of coats, so you buy the right amount without waste or shortage.

Enter length, width, and wall height to get total wall area, then subtract standard openings (21 sq ft per door, 15 sq ft per window). Pick the number of coats and the coverage rating from your paint can (350 sq ft per gallon is typical for latex). Painting an L-shaped room, a hallway, or a stairwell? Switch to individual walls and add each one, or pick exterior to work from the building's perimeter. The result switches between gallons and liters with one click.

How to use

1. Enter the room dimensions: length, width, and wall height.
2. Specify the number of doors and windows to subtract their area from the paintable surface.
3. Choose the number of coats and paint coverage rate, then view the total paint needed in gallons or liters.

When to use

• Buying paint for one room and trying not to over-purchase by a full gallon.
• Quoting an interior repaint job and needing a quick material estimate before walking the site.
• Comparing brands where coverage per gallon differs (240 sq ft for matte vs 400 for some primers).

Result

A room is 12 ft x 14 ft with 8 ft ceilings, 2 doors, and 3 windows. Total wall area is 416 sq ft minus ~77 sq ft for openings = 339 sq ft. At 350 sq ft per gallon with 2 coats, you need about 2 gallons.

FAQ

Why does the calculator subtract 21 square feet for each door?

A standard interior door is 36 by 80 inches, which is 20 sq ft, rounded up to 21 to account for the frame trim. Windows use 15 sq ft as a middle ground between small bathroom windows (8 sq ft) and large picture windows (24 sq ft).

Should I add extra paint for touch-ups?

Round the final number up to the next full gallon. Most painters keep half a quart for future scuff repairs, and stores usually don't take open cans back, so the leftover ends up in the garage either way.

Why does the second coat need the same amount as the first?

It shouldn't, but in practice the second coat uses about 90% of the first because the surface is already sealed. The calculator assumes equal coats to stay conservative, better one extra quart than running out at 5pm on a Sunday.

Does this work for ceilings too?

Yes. Tick the "Include ceiling" box and the calculator adds the ceiling area (room length × width) to the paintable total, so your paint and cost estimates cover the ceiling along with the walls. This assumes a flat ceiling; for a sloped or cathedral ceiling, measure that surface separately and add it on top.

How do I handle textured or rough walls?

Pick the matching option in the "Wall surface" dropdown and the calculator drops the effective coverage for you: light texture adds about 18% paint, heavy texture about 33%, and masonry or stucco about 54%. Leave it on smooth drywall for flat painted walls. If your surface is unusually rough, paint a one-quart test patch and measure what it really covers before buying the full amount.

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