Paint Calculator and Coverage Estimator

Calculate how much paint is needed for your project 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 Size

Paint Estimate:



Use the Paint Calculator to Estimate Coverage

The paint coverage estimation calculator estimates the amount of paint you’ll ned for your decorating project. Simply enter the size of your room and check if you’re also covering your ceiling and the calculator finds the square footage of the walls then estimates the paint and primer needed for that area.

To estimate the paint and primer needed to cover trim or small surfaces, add the size of the room and set the height of the room in inches to the height of the trim. The calculator will convert the inches measurement into feet for you and calculate how many gallons are needed to cover the trim.

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. You can also request an estimate from a professional paint contractor to find out how much painting costs.

How to Estimate The Amount of Paint You Need

Estimate how much paint is needed by finding the square footage of the surface and multiplying by the paint coverage ratio

Paint Gallon Coverage

  • One gallon of paint typically covers a small room, such as a bathroom
  • Two gallons of paint typically cover an average-sized bedroom
  • Three gallons of paint typically cover large rooms, such as a great room.

Measure the Area that Needs to be Painted

Estimating the amount of paint you need involves calculating the square footage of the wall surfaces, then calculating how much paint and primer you need to cover that square footage. Square footage is an area measurement of a space, measured in feet. You can find the square footage of a wall by measuring the length times the height, ie. a 10 ft wide by 9 ft high wall is 10 x 9 = 90 sq ft. Make sure your measurements are in feet before multiplying, it may be easiest to round up to the next foot measurement to avoid working with inches. Use our area calculator to find the area of complicated wall shapes.

If the walls have doors or windows then you can find the square footage of the wall surface by getting the total square footage of the wall, finding the square footage of each door or window, and then subtracting the square footage of the excluded areas from the total measurements.

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, then add the square footages together. To illustrate this, if your wall is not a normal rectangle, break it into different sections and measure the square footage of each section and add the different sections together. Learn more about how to measure irregular walls.

Find the square footage of a complex shape by breaking the area up into normal shapes and adding the square footages together

Once you know the square footage of your walls, add all the square footages together to find the total square footage. Once you know the total square footage you need to cover, you need to find the coverage ratio of your paint. Most professionals use the formula of 350 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, and different application methods, eg. spraying vs. rolling vs. brushing, will cover differently.

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 touchups 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.

Paint Prep Tips

When you’re preparing to paint it’s a good idea to clean the walls with a good cleaner to get rid of any grease or oils that will affect the adhesion of your new paint. TSP (Trisodium Phosphate) is a good all purpose cleaner and does an amazing job at removing all kinds of gunk and leaving a great surface ready to prime. This is no shortcut for not using primer, but will definitely leave a much better finish. You can find TSP at your home center.

Also 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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