Paint calculator

How to estimate how much paint you need in five steps

1. Pick interior or exterior. Choose what you are painting. Inside, you enter the length, width and ceiling height of the room. Outside, you enter the length and width of the house footprint, the wall height and any gables.
2. Count the openings. Enter the number of doors and windows, and tick the box if you are painting the ceiling. The calculator takes the openings out of the wall area, because you do not paint a window.
3. Set coats, coverage and extra. Enter how many coats you plan. Then type the coverage per gallon from the label on your can. The box starts at 350 square feet inside and 300 outside and says check your can. The extra percentage for touch-ups starts at 10.
4. Read the gallons. You see the wall area, the ceiling area, the openings taken out, the net area to paint, the gallons with decimals and the amount rounded up to the nearest quart. Type your own prices if you want a cost range.
5. Compare bids and print. If a painter quotes the job, enter the bid to see the price per square foot to paint. Then download a one-page sheet in English, Spanish or both.

What this calculator does, and what it does not

This page gives you an estimate of how many gallons of paint a room or a house exterior will take. You tell it the size of the surfaces, the number of doors and windows, how many coats and what coverage the can claims. It does the arithmetic and shows every step, so you can follow the numbers and change any one of them.

It is an estimate, not a purchase order. It cannot see the condition of your walls, the color you are covering or how the paint behaves on your surface. We never ask for a phone number, an email or an address, and nothing you type is sent anywhere.

How the wall area is worked out

The walls of a room form a loop, so their total length is the perimeter: twice the length plus twice the width. Multiply the perimeter by the ceiling height and you have the wall area, as if you unrolled the walls into one long strip.

For a room 12 feet by 14 feet with 8 foot ceilings, the perimeter is 2 times 26, which is 52 feet. Times 8 feet, the walls are 416 square feet. The same idea works outside, using the house footprint and the wall height.

Why doors and windows are taken out

Paint does not go on glass, and a door is usually painted separately, often with a different product. So the calculator subtracts the openings from the wall area. It counts a door as 21 square feet, which is 3 feet by 7 feet, and a window as 15 square feet, which is 3 feet by 5 feet. Those are common round sizes, and they are about right for a typical home, not a measurement of yours.

In the room above, one door and two windows come to 21 plus 30, which is 51 square feet. Taking them from the 416 gives a net of 365 square feet to paint. If your windows are much larger or smaller, the real number will move a little, and a small difference rarely changes the number of cans.

From square feet to gallons

The label on the can gives a coverage, the number of square feet one gallon covers in one coat. Take the net area, multiply by the number of coats, divide by the coverage, and add the extra percentage for touch-ups.

For the room above: 365 square feet times 2 coats is 730. Divided by 350 square feet per gallon, that is about 2.09 gallons. Add 10 percent and you get 2.2943 gallons. The calculator then rounds that up to the nearest quart, which is a quarter of a gallon, so it shows 2.50 gallons. A quart is the smallest practical amount to buy, and rounding up keeps you from stopping a wall short.

A worked exterior example with gables

Take a house footprint of 40 feet by 30 feet with 9 foot walls. The perimeter is 140 feet, so the walls are 140 times 9, which is 1,260 square feet. A gable is the triangle of wall under the peak of the roof. Its area is half the base times the rise. With two gables, each with a 30 foot base and an 8 foot rise, each one is 120 square feet, and together they are 240.

The surfaces add up to 1,500 square feet. Two doors and ten windows take out 42 plus 150, which is 192, leaving a net of 1,308 square feet. For two coats at 300 square feet per gallon with 10 percent extra, that is about 9.5920 gallons, and the calculator shows 9.75. Siding texture, brick or stucco can change the real coverage a lot, so check your can and ask your supplier.

Coverage is on the can, and it varies

Coverage depends on the product and on the surface. Smooth, sealed walls take less paint. Rough, porous or textured surfaces, such as stucco, raw wood or fresh drywall, drink more and spread fewer square feet per gallon. Dark colors over light ones, or the reverse, can also call for more.

That is why the coverage box is a number you type. We start it at 350 inside and 300 outside as a common middle ground, and we label it check your can. Read the figure printed on the label of the product you picked, type it in, and the result follows it.

Primer, coats and the second coat

The coats box counts every layer you plan. Many jobs use two coats of the finish. If you will also prime, a primer layer is usually bought and counted on its own, since it comes in its own can with its own coverage. You can run the calculator a second time with one coat and the primer coverage to see that amount.

A first coat often looks patchy and a second evens it out. Changing a color, patching a wall or painting new drywall tends to need more coats. Your supplier or the label can say how many a product usually takes.

Ceilings, trim and leftovers

Tick the ceiling box and the calculator adds the ceiling area, which is the length times the width. For the 12 by 14 room that would be 168 square feet more. Ceilings are often a different paint, so you may want to run them as a separate job.

Trim, baseboards, door frames and crown molding are not included. They are narrow, they are often a different finish and they are better measured by hand. The extra percentage covers touch-ups, spills and a little left in the can for later, because the same color is hard to match afterward. Keep the leftover, sealed, with the color name on the lid.

Older homes and preparation

Homes built before 1978 may have lead-based paint. A federal rule applies to paid work that disturbs paint in older homes, and the tool links to the page of the Environmental Protection Agency on it. We give no advice here; the link is the place to read what applies.

Preparation, such as cleaning, scraping, sanding, patching and priming, changes the result and the cost. We do not estimate it. Whether preparation is in a bid is one of the things the bid check lists.

Comparing painting bids

The bid check divides each total by the paintable area, so you see a figure per square foot for every bid. A larger house at a higher total can still cost less per square foot than a small one, and the comparison shows that.

That figure only helps if the bids cover the same work. Ask every painter the same questions:

• Surface prep and patching: who does it, and how much is included?
• Primer: is it included, and on which surfaces?
• Number of coats.
• Ceilings: in the price, or only walls?
• Trim and doors: painted or left out?
• Cleanup: protecting floors and furniture, and hauling away the mess.
• Is the paint brand and color named in the bid?
• Is there a written warranty on the work?

Print the one-page sheet, in English, Spanish or both, and bring it to each quote so every painter answers the same list.

Your answers and your privacy

The calculator runs in your browser. It has no place to type a phone number, an email or an address, nothing you enter is sent to a server, and nothing is saved when you close the page. Print the sheet if you want to keep the numbers.

Frequently asked questions