Estimate Paint And Primer Coverage - Inch Calculator

Calculate how much paint and primer you need by entering the project area or the dimensions of your room below.

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Results: Paint Estimate

Results: Paint Estimate

Paint:	- - - Result Unit gallons quarts liters
Primer:	- - - Result Unit gallons quarts liters
Total Area:	- - Result Unit sq ft sq m

*Paint estimate is per coat Results: Paint Estimate

Paint:	- - - Result Unit gallons quarts liters
Primer:	- - - Result Unit gallons quarts liters
Total Area:	- - Result Unit sq ft sq m

*Paint estimate is per coat Results: Paint Estimate

Paint:	- - - Result Unit gallons quarts liters
Primer:	- - - Result Unit gallons quarts liters

*Paint estimate is per coat Learn how we calculate this below Share Icon Share Results Embed IconAdd This to Your Site ×Close dialog

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• Paint Calculator
• How to Calculate How Many Gallons of Paint You Need
• Step One: Measure the Space
• Step Two: Calculate the Paint Needed
• Paint Coverage Chart
• How to Estimate Paint for Trim
• How to Estimate Exterior Paint
• Frequently Asked Questions

Person Icon By Joe Sexton

Joe is the creator of Inch Calculator and has over 20 years of experience in engineering and construction. He holds several degrees and certifications.

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Sarabeth is an expert in the home and garden industry and was formerly a certified kitchen and bathroom designer. She is a subject matter expert in home improvement and is often quoted in notable publications.

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Sexton, J. (n.d.). Paint Calculator. Inch Calculator. Retrieved February 19, 2026, from https://www.inchcalculator.com/paint-calculator/

How to Calculate How Many Gallons of Paint You Need

When you’re painting a room, a fence, or your whole house, you might be wondering how many gallons of paint you’ll actually need. Paint is costly, and while you do want a small amount extra for touch-ups later, you don’t want to order much more than you need, as it is not returnable.

You can calculate how many gallons you need using the calculator above or by following a few simple steps.

Step One: Measure the Space

The first step is to measure the space and calculate the total area you will be painting. Measure the width and height of each wall in feet.

Multiply the width by the height to calculate the area of the wall in square feet. Then, add the square footage of each wall to calculate the total square feet.

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.

Step Two: Calculate the Paint Needed

Divide the total square feet by the paint coverage to find the total gallons of paint needed per coat. One gallon of typical latex paint usually covers 350 to 400 square feet per coat, but this can vary from product to product.

It’s also important to note that different application methods, such as spraying, rolling, or brushing, will cover differently.

You’ll need to round up to the nearest full gallon or quart. It is not a bad idea to have some leftover paint at the end of a project since it can be used for touch-ups, particularly with some shades that can be difficult to match or that can vary slightly from lot to lot.

You can use the quick reference table below to get an estimate how many gallons of paint you’ll need for typical rooms.

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Paint Coverage Chart

The table below shows approximately how much paint is needed for average-sized rooms.

Amount of paint needed to cover the average-sized room, using a standard latex paint

Room Size	Gallons of Paint Needed
small room (8′ x 8′)	1 gallon
medium room (12′ x 12′)	2 gallons
large room (18′ x 18′)	3 gallons
bathroom	1 gallon
kitchen	1-2 gallons
bedroom	2 gallons
family room	3 gallons

This does assume that the paint you are using can cover in one coat. If you are going from light to dark or dark to light, you may need either a tinted primer and one to two coats of paint or two to three coats of paint without primer to get the desired color.

Paints that contain paint and primer in one will usually cover in one coat, but always check the brand and type of paint you’re using for recommendations, particularly for bright or dark colors. If you’re painting new drywall, then it’s a good idea to apply a coat of primer first.

How to Estimate Paint for Trim

Here’s a tip: estimate the paint and primer needed to cover trim or small surfaces by taking the linear footage of the room – or the number of feet around the perimeter, and multiplying this by the height of the trim. To make it more accurate, measure the perimeter in inches or divide the linear feet by 12 before multiplying.

Once you have the total square inches, divide by 144 to get the square feet. This can be an easier method than attempting to find the height in feet of some trims, like a pencil, which may be less than 1 inch tall.

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 0.33 feet tall.

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

You might also be interested in estimating wallpaper for your space.

How to Estimate Exterior Paint

You can estimate the exterior paint you’ll need just like interior projects. Start by measuring each exterior wall of the home, then calculate the square footage of each one.

For walls with a gable, measure the square portion and the gable portion separately. You might find a triangle area calculator helpful for finding the square footage of the gable.

Then, add the square footage of each area together. Subtract the square footage of any doors and windows that you won’t be painting from the total square footage.

Consult the directions on the specific product you’ll be using for a coverage estimate.

Keep in mind that walls with porous surfaces such as concrete, brick, or rough wood will soak up much more paint than a smooth surface. We suggest ordering more paint than you estimate to cover these surfaces.

Or speak to the paint retailer about what they recommend for painting these surfaces. Likewise, a home with wood siding that is older will require more paint than a home with new wood siding.

When making dramatic color changes, you might also need an additional coat of paint to get adequate coverage; be sure to account for this in your estimate.

You can also use our fence stain and deck stain calculators to estimate how much you’ll need.

Frequently Asked Questions

How much does 1 gallon of paint cover?

This can vary depending on the type of paint and the surface you are covering. The general rule of thumb, however, is that 1 gallon of latex paint will cover 350 to 400 sq ft.

How much paint do you need for a 12x12 room?

Most likely, you will need two gallons of paint to cover a room of this size. However, things like windows and doors, the color of the paint, and the current color of the walls can all influence the total amount you will need.

Do you need primer?

This depends a lot on the project. For cedar or redwood, vinyl, or big color changes – from very light to dark or dark to light, as well as to cover stains from things like mold, then yes, primer is required. Otherwise, it may not be necessary, depending on the paint you choose.