How do I calculate how much paint I need?

Estimate paintable square footage, multiply by the number of coats, add a waste factor, then divide by the paint coverage rate per gallon.

How much wall area does one gallon of paint cover?

Many interior paints cover about 300 to 400 square feet per gallon depending on surface texture, color change, and product quality. Check the paint can label for the final coverage rate.

Interior painting cost calculator

Estimate paint gallons, material cost, and labor before you buy.

Enter room dimensions or a known square footage. CoatWise estimates paint coverage, gallons to buy, supplies, labor, and total project cost.

Paintable area

Room dimensions Total square feet

Room length, ft Room width, ft Wall height, ft Rooms like this

Doors to subtract Windows to subtract Include ceiling Include primer coat

Paint and cost assumptions

Finish coats Coverage per gallon, sq ft Paint price per gallon Primer price per gallon Supplies budget Waste factor, %

Labor estimate

Labor rate per sq ft Minimum labor charge

Set labor to 0 for a DIY material-only estimate.

Paint roller, tray, and color swatches in a clean interior room

Measure walls first. Then adjust coats, coverage, waste, and labor to match the project.

Cost breakdown

Materials, labor, and coverage

Line item	How it is estimated	Amount

How to use this interior painting cost calculator

Start with room dimensions if you are pricing a bedroom, living room, office, hallway, or apartment interior. Use total square feet if you already measured the wall area from a floor plan or contractor quote.

When to include the ceiling

Include the ceiling when you are painting the whole room or changing from a darker ceiling color. Keep it off when the project is only walls.

What affects interior painting cost?

Paint cost changes with room size, number of coats, paint quality, surface texture, repairs, trim detail, local labor rates, and whether primer is needed. A simple repaint is usually easier to estimate than dark-to-light color changes or textured surfaces.

DIY vs professional painting

For DIY, set labor rate to 0 and focus on paint, primer, tape, rollers, trays, drop cloths, and repairs. For a professional estimate, use a local labor rate per square foot and a minimum labor charge.

Related calculators

Plan the whole paint job

Paint CalculatorGeneral gallons and coats estimator Paint Coverage CalculatorCoverage by gallons and square footage Paint Cost CalculatorMaterial, supplies, and labor costs Exterior Paint CalculatorSiding, trim, doors, and windows Paint Calculator by Square FeetStart from measured square footage

Interior painting calculator FAQ

How many square feet does a gallon of paint cover?

Many interior paints cover about 300 to 400 square feet per gallon. Rough surfaces, dramatic color changes, and cheaper paints may cover less.

Should I round paint gallons up?

Yes. Buy full gallons or the closest can size available. Rounding up also gives you paint for touch-ups.

Does the calculator include trim?

The main estimate focuses on walls and optional ceiling. Add trim by increasing paintable square feet or supplies if your project includes baseboards, doors, crown molding, or window casing.

Is this a contractor quote?

No. It is a planning estimate. Local labor, repairs, prep work, paint brand, and room condition can change the final price.