Paint Coverage Calculator

What this paint coverage calculator does

Most paint calculators answer one question: how much paint do I need? This page answers two. The first tab turns a room size or a total area into gallons to buy. The second tab starts from paint you already own and shows how many square feet it will cover.

Both tabs use the same inputs: the surface type, which sets the coverage rate, the number of coats, roller or sprayer, and a waste allowance. The calculator shows each step of the arithmetic and two charts, one for coats and one for surface type, because those are the two choices that change the answer most. If you also want a primer coat or a 3D room preview, use the paint calculator instead. To measure the area first, use the square footage calculator. More tools are listed on the painting calculators page.

How to use the paint coverage calculator

1. Choose a tab. Use “How much paint do I need” to plan a purchase. Use “How far will my paint go” to check what paint you already have can finish.
2. Enter your measurements. Pick feet or meters, then enter a room size or a total area. Tap the small i beside any field to see what to measure.
3. Pick the surface. The surface sets the coverage rate. If your can prints a different number, choose Custom and type it in.
4. Set the coats and method. Two coats is the usual plan for new paint or a color change. Choose sprayer if you will spray.
5. Read the result. Check the paint to buy and the can mix, then the step-by-step math and the two charts. Everything updates as you type.

How much does a gallon of paint cover?

The figure printed on most paint cans is about 350 to 400 square feet per gallon for one coat on a smooth, sealed, previously painted surface. With two coats, a gallon covers about half of that, or 175 to 200 square feet. For planning, use 350 for average interior walls, and use the lower end of any range on the can. The table scales the same range to common can sizes.

Rough, textured or unprimed surfaces take more paint, so coverage can fall to 200 to 300 square feet per gallon. The next section lists planning rates by surface.

Paint coverage per gallon by surface

These are the planning rates the calculator uses. They are typical averages, not guarantees. If the data sheet for your paint or primer gives a different rate, use that one.

How to calculate paint coverage

The method is the same for any room.

1. Find the wall area. Wall area = 2 × (length + width) × height.
2. Subtract openings. This calculator removes 21 square feet for each door (3 × 7 feet) and 15 square feet for each window (3 × 5 feet).
3. Add the ceiling if you are painting it. Ceiling area = length × width.
4. Multiply by the number of coats. Two coats doubles the area you must cover.
5. Divide by the coverage per gallon, then multiply by 1.10 for a 10 percent allowance and round up to the next quart.

Worked examples

Example 1: how much paint to buy

A 14 by 12 foot room with 8 foot walls, one door and two windows, walls only, two coats, 350 square feet per gallon and a 10 percent allowance. These are the default values on the first tab.

• Wall area: 2 × (14 + 12) × 8 = 416 square feet.
• Openings: 1 door × 21 + 2 windows × 15 = 51 square feet, so the paintable wall is 365 square feet.
• Two coats: 365 × 2 = 730 square feet of paint to apply.
• Gallons: 730 ÷ 350 = 2.09, and with 10 percent waste 2.29 gallons.
• Rounded up to whole quarts: 2.5 gallons, which is two 1-gallon cans and two quarts.

Example 2: how far leftover paint goes

You have three 1-gallon cans, plan two coats at 350 square feet per gallon, and keep 10 percent back for touch-ups. These are the default values on the second tab.

• Usable paint: 3 ÷ 1.10 = 2.73 gallons.
• One coat would cover 2.73 × 350 = 955 square feet.
• Two coats: 955 ÷ 2 = 477 square feet of finished surface.
• A 12 by 12 foot room with 8 foot walls, one door and one window has 348 square feet of wall, so the paint finishes about 1.4 rooms.

For other room sizes and a primer coat, see the paint calculator.

Why paint coverage changes

Coverage is not a fixed property of the paint. It changes with the surface and the way you apply it.

• Porosity. Bare drywall, bare wood and patched spots absorb the first coat. Prime them first, or expect less coverage.
• Texture. Orange peel, knockdown, stucco and brick have more surface than a flat wall. Use a lower rate.
• Color change. Going from a dark color to a light one often needs an extra coat or a tinted primer.
• Application method. A roller on a smooth wall is the baseline. Sprayers lose paint to overspray, so the calculator adds 20 percent when you pick one. That is a typical allowance, and the real figure depends on the sprayer and the setup.
• The product. Many cans quote the same 350 to 400 square feet, and a premium paint does not necessarily stretch further. Primer coverage also differs from finish paint, so read the primer can.

The coats chart shows the cost of one more coat: three coats need half again as much paint as two.

Paint coverage in liters and square meters

Outside the United States, cans list coverage as square meters per liter. One square foot per US gallon equals about 0.02454 square meters per liter, and a US gallon is 3.785 liters. So 350 square feet per gallon is 8.59 square meters per liter.

To use a metric can here, divide the square meters per liter on the label by 0.02454. A can that quotes 12 square meters per liter works out to about 489 square feet per gallon. Choose Custom and type that in, or switch the unit to meters and enter your room in meters. Results show both gallons and liters. For the official unit definitions, see the NIST unit conversion resources.

Before you buy

• Read the can. The coverage printed for your exact product beats any average, including the ones on this page.
• Buy all the cans for one color at once, so the color stays consistent from wall to wall.
• Check the age of the house. Paint in homes built before 1978 may contain lead. Paid contractors who disturb it must follow the EPA’s lead-safe rules, and the same precautions make sense for do-it-yourself work. See the EPA renovation, repair and painting program before you sand or scrape.

How this calculator works and what it assumes

• It runs in your browser, so your measurements are not sent anywhere.
• Walls are 2 × (length + width) × height, with the same height on every wall. The ceiling is flat and equals length × width. Doors are 21 square feet and windows are 15.
• Coverage rates are planning averages. The sprayer allowance is 20 percent and the default waste allowance is 10 percent.
• The result is rounded up to whole quarts. The suggested mix groups the total into pails, gallons and quarts, and when 4 gallons or more are left after full pails it rounds up to another pail.
• Trim, doors, baseboards, gables and soffits are not included. Work them out separately.
• The cost is the gallons to buy times the price per gallon you enter. It covers paint only.

Built and maintained by Shivam, a software engineer. This is a planning tool, not a contractor’s quote. Change log: October 11, 2026, first published with two modes, can-size order, step-by-step math and two charts.

Paint coverage FAQs

These calculators give planning estimates only. They do not replace the product data sheet or advice from a licensed contractor. Read our Disclaimer for details, or contact us if you spot a mistake.