Paint Calculator

Estimate interior paint for one room or several rooms, including walls, ceilings, doors, windows, trim, coats, coverage, and a touch-up buffer. Get exact gallons plus a practical buy list.

Reviewed and updated July 7, 2026

Use it when you want to know
  • How many gallons to buyTurn room measurements into exact gallons and rounded containers.
  • Walls, ceilings, and trimKeep wall paint, ceiling paint, and trim paint separated when they use different finishes.
  • Avoid the one-gallon gambleSee when two coats, color changes, texture, or touch-ups call for more paint.
Calculator

How much paint do you need?

Start with room length, width, height, coats, and coverage. Add more rooms, openings, ceilings, trim, and primer only when you need a tighter shopping list.

Rooms

Add each room that will use the same wall paint color and finish.

Paint coverage and coats

Most interior paints list coverage per gallon per coat. Use the product label when you know it.

Doors and windows

Ceiling, trim, and primer

Container rounding

Guide

How do you calculate how much paint you need?

The useful estimate is not floor square footage. For interior rooms, start with wall area, multiply by coats, divide by paint coverage, then round into real containers with a small touch-up buffer.

Should you subtract doors and windows?

Subtracting doors and windows gives a tighter estimate. A common shortcut is about 20 square feet per standard door and 15 square feet per average window. If your measurements are rough, leaving openings in the total can act as a built-in buffer.

How many coats should you plan for?

Two coats is the safest default for most interior repainting. One coat may work for very similar colors with a high-quality paint, but strong color changes, patches, new drywall, stains, or textured walls usually need primer, more paint, or both.

How much does a gallon or quart cover?

Many interior wall paints cover roughly 350 to 400 square feet per gallon per coat. A quart covers about one quarter of a gallon, often around 85 to 100 square feet depending on product and surface. Always use the label when you know the exact paint.

How should you estimate trim and ceiling paint?

Ceilings are usually the room length multiplied by the room width. Trim can be estimated by multiplying linear feet by average trim width, then converting inches to feet. Keep trim paint separate because it often uses a different sheen than wall paint.

Basic formulagallons = area x coats x buffer / coverage

Example: a 10 ft by 10 ft room with 8 ft walls has 320 sq ft of wall area before openings. Two coats with a 10% buffer at 350 sq ft per gallon needs about 2.01 gallons before door and window deductions.

The default coverage and container logic are planning assumptions, not product guarantees. Compare the result with your paint label and retailer guidance such as Lowe's paint calculator, Sherwin-Williams paint calculator guidance, Benjamin Moore's paint calculator, and PaintCare's paint calculator note.

Common paint estimating mistakes

Do not use floor square footage as wall area, forget the second coat, mix wall and trim finishes together, or buy so tightly that there is nothing left for missed spots and touch-ups.

When primer matters

Use primer for new drywall, bare wood, stains, patched areas, strong color changes, glossy surfaces, and surfaces where the paint label recommends it. Primer coverage is often lower than paint coverage.

Why one gallon can be risky

A single gallon may cover a small bedroom for one coat, but two coats on a typical bedroom often pushes past that. Running short can also create color matching problems if you need another batch later.

Keep the leftover useful

Label leftover paint with the room, brand, color, finish, and date. Store it sealed and away from freezing or extreme heat so future touch-ups are easier.

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FAQ

Paint calculator questions

How much paint do I need for a 10x10 room?

A 10 by 10 room with 8-foot ceilings has about 320 square feet of wall area before doors and windows. At 350 square feet per gallon, two coats usually need about 1.8 gallons before a buffer, so buying 2 gallons is a practical starting point.

Is one gallon enough for a bedroom?

One gallon can be enough for a small room with one coat, or for some very small rooms with openings deducted. For a typical bedroom with two coats, 1 gallon is often risky. Measure the wall area and check the coverage on the paint label.

Does this paint calculator include two coats?

Yes. The default is 2 coats for walls, ceilings, and trim because most interior repainting projects need two coats for even color and durability. You can change the coat count if your product or project is different.

Should I include the ceiling?

Include the ceiling if you plan to paint it. Ceiling paint is usually a separate finish and color, so the calculator keeps ceiling gallons separate from wall paint when ceiling painting is selected.

Should I subtract doors and windows?

Subtracting doors and windows makes the estimate tighter. Leaving them in creates a small extra buffer, which can be useful for textured walls, touch-ups, or uncertain measurements.

How much paint should I keep for touch-ups?

A 10% buffer is a good default for small measurement errors, roller loading, texture, and future touch-ups. Keep the leftover paint labeled with the room, color, finish, and date.

What coverage number should I use from the paint can?

Use the coverage listed on the paint label or product page. Many interior paints cover roughly 350 to 400 square feet per gallon per coat, but rough surfaces, deep color changes, and application method can lower real coverage.

Do I need primer?

Primer is often helpful for new drywall, bare wood, stains, repairs, strong color changes, glossy surfaces, or patched areas. This calculator can estimate primer separately, but you should follow the paint and primer label directions.