Paint Calculator

Enter your room dimensions to find exactly how many gallons of paint you need, accounting for doors, windows, and multiple coats.

Paint Calculator

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Room length (ft)

Room width (ft)

Ceiling height (ft)

Doors

Windows

Number of coats

Gallons needed

1.99

Paintable area

348 sq ft

Suggested purchase

2 gallons

Assumes standard coverage of 350 sq ft per gallon, and 21 sq ft per door and 15 sq ft per window.

The formula

Wall area = 2 x (Length + Width) x Height Paintable area = Wall area − (Doors x 21) − (Windows x 15) Gallons = (Paintable area x Coats) / 350

Example

A 12x12 room with 8 ft ceilings, 1 door, 1 window, 2 coats: wall area = 384 sq ft, paintable = 348 sq ft, gallons = (348 x 2) / 350 ≈ 1.99 gallons - round up to 2 gallons at the store.

Step-by-step guide

Enter your room's length, width, and ceiling height.
Enter the number of doors and windows - their area gets subtracted automatically using standard sizes.
Enter the number of coats - 2 is standard for a color change or high-traffic wall.
Round up to the nearest whole gallon when buying, since paint is sold in fixed can sizes.

Choosing how many coats

One coat is sometimes enough for a fresh coat of the same or a very similar color over a well-prepared surface. Two coats is the standard recommendation for most color changes, new drywall, or when covering a darker color with a lighter one - it evens out roller marks and gives more uniform coverage. Going from a dark to a very light color, or painting bare drywall, may need a tinted primer coat first, which this calculator doesn't include separately - add roughly one more "coat" worth of gallons if priming.

Common mistakes

Forgetting the ceiling - this calculator covers walls only; add the room's square footage (length x width) separately if you're painting the ceiling too.

Assuming all paint covers the same area per gallon - coverage varies by brand, sheen, and surface texture; check the specific product's label for its actual coverage rate.

Frequently asked questions

Should I round up or down on my paint purchase?

Always round up. Running short mid-job means a store trip with a wet edge already drying, and matching a tinted color exactly on a second trip isn't guaranteed if it's a custom mix.

Does this account for texture or trim?

No - heavily textured walls (like popcorn ceilings or rough stucco) absorb more paint than the standard coverage rate assumes, so add extra for those surfaces. Trim and baseboards are a separate, much smaller paint quantity.

How much paint is left in a "leftover" can?

If you're using partially-used cans, estimate their remaining volume and subtract it from the total gallons calculated here before buying more.

Do I need primer?

Primer is commonly recommended for bare drywall, a major color change (especially dark to light), stain-blocking, or covering glossy surfaces. Many "paint and primer in one" products reduce but don't always eliminate the need for a separate primer coat in these situations.

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