Paint Calculator and Coverage Estimator

Calculate how much paint you need by entering your room’s dimensions. Estimate how many gallons are needed based on average paint/primer coverage. Optionally include the ceiling in your estimate.

Room Dimensions

Paint Estimate:

  gallons of wall paint
  gallons of ceiling paint
  gallons of primer
Paint Area
  wall square feet
  ceiling square feet
  total square feet


The paint coverage estimation calculator estimates the amount of paint you’ll need for your decorating project. Simply enter the size of your room and the calculator finds the square footage of the walls, then estimates the paint and primer needed for that area.

It doesn’t matter if you’re a do-it-yourselfer or an experienced professional, the paint calculator is an extremely valuable tool for estimating paint coverage.

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How Many Gallons of Paint Do You Need?

gallon paint cans with various colors of paint

Calculating how many gallons of paint or primer are needed for a project can be done in a few simple steps. The easiest option is to use the calculator above. If you want to calculate yourself, follow the steps below to easily estimate the paint needed for your project.

Simple Paint Gallon Coverage Estimates

By far the easiest way to estimate how many gallons of paint are needed for a project is to consult this quick reference table. This table shows the estimated amount of paint needed for average sized rooms.

One gallon of typical latex paint usually covers 350 to 400 square feet of wall area.

Amount of paint needed to cover the average sized room, using a standard latex paint
Room Size Gallons of Paint Needed
small room (8’x8′) 1 gallon
medium room (12’x12′) 2 gallons
large room (18’x18′) 3 gallons
bathroom 1 gallon
kitchen 1-2 gallons
bedroom 2 gallons
family room 3 gallons

Measure the Area that Needs to be Painted

By far the most accurate method of calculating paint and primer for a project is to measure the surfaces to be painted and use the coverage estimate for the specific paint being used.

Step One: Measure the Walls

The first step in estimating paint material is to measure the walls or ceilings that are going to be painted. Measure the length and height of each wall in feet and write them down. It may be easiest to round up to the next foot measurement for measurements that contain partial feet.

Step Two: Calculate Square Footage of Each Surface

The next step in the process is to calculate the square footage of the walls and ceilings. Square footage is an area measurement of a space, measured in feet, and we have a simple calculator to help with these calculations.

For each set of measurements from step one, multiply the width and height together to get the square footage. Make sure your measurements are in feet before multiplying. Write down the square footage of each wall.

For example, let’s find the square footage of a wall that is 10 ft. wide by 9 ft. high.

sq. ft. = 10 ft. × 9 ft.
sq. ft. = 90 sq. ft.

Pro Tip: use an area calculator to find the area of complicated wall shapes.

For walls that have large banks of doors or windows, consider subtracting the area of those from the wall square footage to avoid ordering too much paint. To do that, measure the length and height of each door and window and multiply to find the square footage. Then, subtract the door and window square footage from the wall square footage to find the area that needs paint.

If the walls are not simple rectangles or are complex then consider breaking the wall into smaller sections and calculate the square footage of each section individually. To illustrate this, if your wall is not a normal rectangle, break it into different sections and measure the square footage of each section. Learn more about how to measure irregular walls.

diagram showing how to measure a complex area
Illustration showing how to break up a complex wall shape into smaller pieces to measure.

Step Three: Add Square Footages Together to Find the Total

Once you know the square footage of each wall, add them together to find the total square footage. If you had split complex walls into several surfaces then be sure to add each surface to get the total.

For example, let’s find the total square footage for 2 walls that are 120 sq. ft. and 2 walls that are 150 sq. ft.

total sq. ft. = 120 + 120 + 150 + 150
total sq. ft. = 540 sq. ft.

Step Four: Calculate Paint Coverage

The final step is to find the coverage ratio of your paint and calculate the number of gallons needed to cover the total square footage. Most professionals use the formula of 350 to 400 square feet of wall coverage per gallon of paint and 200 square feet of wall coverage per gallon of primer.

It’s important to note that different types and manufacturers may cover more or less area. It’s also important to note that different application methods such as spraying, rolling, or brushing will cover differently.

Your paint vendor should be able to tell you the coverage for your selected paint, and it’s often indicated on the container.

Divide the total square footage by the coverage rate to find the number of gallons needed.

For example, let’s find the paint needed to cover 540 sq. ft. using a paint that covers 350 sq. ft. per gallon.

gallons = sq. ft. ÷ coverage
gallons = 540 ÷ 350
gallons = 1.54 gallons

How to Estimate Paint for Trim

Here’s a tip: estimate the paint and primer needed to cover trim or small surfaces by adding the size of the room and set the height of the room in inches to the height of the trim.

You can also estimate trim using the measurement method above. Start by measuring the height of the trim in inches, then convert that to feet. For example, trim that is 4 inches tall is .33 feet tall.

Then multiply the height by the length of trim to find the square footage. Then follow the rest of the steps above to estimate paint needed to cover that square footage.

Paint Estimation Tips

It may be a good idea to order 10-20% extra, probably an extra quart or gallon depending on your project, to allow for differences in coverage and to have extra paint for touch-ups down the road. If you are fairly close to an even gallon on a small project and want to save some money, consider ordering a quart for your overage.

Don’t forget to estimate the amount of other supplies needed for a painting project. Be sure to grab plenty of tarps and use a good blue masking tape to tape off any surfaces for a clean paint job. Finally, make sure you choose a good brush and rollers, spending an extra dollar or two on these will have just as much impact on your finish as the quality of the paint itself.

Use a paint calculator such as the one above to estimate the amount of material needed to cover your room so you can ensure you purchase just the right amount of paint to save money and avoid a headache later.


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