Paint Calculator

Find out exactly how much paint to buy for any room with our free paint calculator, in seconds.

One gallon of paint covers about 350 square feet. A 12×14 room with 8-foot walls needs about 2 gallons for two coats.

How Much Paint Do I Need?

Most rooms need more paint than people guess. A 12×14 bedroom with 8-foot walls has 365 square feet of wall space after you subtract one door and two windows. That takes about 2.09 gallons for two coats, so you would buy 2 gallons and 1 quart.

One gallon of paint covers about 350 square feet with one coat. But almost every room needs two coats for rich, even color. That means a small 10×10 room needs about 1.62 gallons for two coats, and you would buy 2 gallons.

The paint calculator above does all of this math for you. Type in your room size, doors, and windows. Pick how many coats you want. It tells you the wall area, the exact gallons needed, and what to buy at the store.

Buying the right amount matters. Too little paint means a second trip to the store, and the new can might not match the old one. Too much paint wastes money and sits in your garage for years. A quick calculation before you shop saves both problems.

Paint Chart by Room Size

This chart uses 8-foot walls, 1 door, and 2 windows. Your room may be a little different, so use the paint calculator for your exact numbers.

Notice how two coats almost doubles the paint. That second coat is what gives you deep, even color with no thin spots. Skipping it is the most common reason a paint job looks unfinished.

How to Use This Calculator

Start by picking feet or meters at the top of the tool. Then type in your room length, width, and wall height. Most American rooms have 8-foot ceilings, and that is the default.

Next, count your doors and windows. Include closet doors. Each door removes about 21 square feet from the paintable area. Each window removes about 15 square feet.

Pick your coats. Two coats is the default because it gives the best finish for most rooms. If you also want to paint the ceiling, check the box. The ceiling result shows up on its own card because ceilings often use a different paint, usually flat white.

Your results update the moment you type. The big card tells you what to buy, like “2 gallons + 1 quart.” The smaller cards show your wall area in square feet and the exact gallons needed.

How We Calculate It

The math is simple. First we find your paintable wall area:

Wall area = 2 x (length + width) x height – (doors x 21) – (windows x 15)

Then we figure out the paint:

Gallons = wall area x coats / 350

Here is a worked example. Take a 12×14 room with 8-foot walls, 1 door, and 2 windows, painted with 2 coats.

Wall area = 2 x (12 + 14) x 8 – (1 x 21) – (2 x 15) = 416 – 21 – 30 = 365 square feet.

Gallons = 365 x 2 / 350 = 2.09 gallons.

To decide what to buy, we split 2.09 into 2 whole gallons plus a leftover of 0.09 gallons. That leftover times 4 is 0.36, rounded up to 1 quart. So you buy 2 gallons and 1 quart. In liters, that is 2.09 x 3.785 = 7.9, rounded up to 8.0 L.

When the leftover needs 3 or more quarts, we just round up to another full gallon. Gallons are cheaper per quart than single quarts, so this saves you money.

How Many Coats of Paint Do You Need?

Two coats is the safe answer for most rooms. The first coat soaks into the wall and covers the old color. The second coat gives you the true, rich color from the paint chip.

You might need three coats when you paint a light color over a dark color. Choosing the right shade? Browse our bedroom color ideas for inspiration. White over navy, for example, almost always needs three coats. Red and bright yellow paints are also known for needing an extra coat because their pigments cover less well.

New drywall always needs special care. Fresh drywall drinks paint fast. Use a primer first, then two coats of paint. Without primer, you might need three or four coats, which costs more than the primer would have.

One coat can work when you refresh a wall with the same color and the old paint is in good shape. Even then, look closely after the first coat dries. Thin spots and roller marks often show up, and a second coat fixes them.

Do You Need Primer?

Primer is a base coat that helps paint stick and cover better. You need it in a few clear cases. Use primer on new drywall, on bare wood, and when you paint over stains or dark colors.

Primer also helps when you switch from oil-based paint to latex paint. The old oil surface is slick, and new paint can peel off it. A bonding primer gives the new paint something to grip.

You can often skip primer when the walls are already painted with latex paint in good shape and you pick a similar color. A light gray over an old off-white, for example, usually covers fine with two coats and no primer.

Paint and primer in one is popular, but read the label with care. These paints are thicker and cover a bit better than plain paint. They are not the same as a real primer coat. On new drywall or dark colors, use a separate primer anyway.

Primer math is easy. Figure it the same way as paint, but plan for one coat. A 12×14 room needs about 1.04 gallons of primer, so buy 1 gallon and 1 quart.

Gallons vs Quarts: Buying Smart and Saving Money

Paint gets cheaper per quart when you buy bigger cans. A gallon almost always costs less than four separate quarts. So when your leftover paint needs 3 quarts, just buy another gallon instead. You pay less and get more paint for touch-ups.

Quarts make sense for small jobs. An accent wall in a 12×14 room is about 112 square feet. One coat needs 0.32 gallons, so a single quart (0.25 gallons) is close but a little short. Buy two quarts or one gallon to be safe.

Always buy a little extra for touch-ups. Walls get scuffed. Keep a small jar of each wall color with the room name on the lid. Store it inside your house, not the garage, so heat and cold do not ruin it.

Buy all your paint at once, and check the batch numbers on the cans. Paint mixed on different days can differ just enough to show on the wall. If you must buy more later, mix the old and new paint together in a bucket before you start. Painters call this boxing, and it blends any small color differences.

Tackling a workspace makeover? See our small home office ideas for paint colors that boost focus in tight spaces.

How to Measure a Room for Paint

Grab a tape measure and a notepad. Measure the length of each wall at the floor and write down the two longest numbers as your length and width. Rooms are rarely perfect rectangles, so the longest numbers keep you from coming up short.

Measure wall height from the floor to the ceiling. Do not guess. Many older homes have 9-foot ceilings, and that extra foot adds a lot of wall area. A 12×14 room with 9-foot ceilings has 417 square feet of wall instead of 365.

For rooms that are not rectangles, break the room into rectangles. Measure each section, figure each area, and add them up. L-shaped rooms are just two rectangles put together.

For the ceiling, multiply length times width. A 12×14 ceiling is 168 square feet. Two coats need 0.96 gallons, so buy 1 gallon of ceiling paint.

Doors and windows are simple. Count them and let the calculator subtract them. A standard door is about 21 square feet and a standard window is about 15 square feet.

Planning a full room refresh? Our coastal decor ideas show how paint color sets the mood for the whole space.

Common Paint Mistakes

The biggest mistake is not subtracting doors and windows. A room with 3 doors and 4 windows has 123 square feet you will never paint. That is more than a third of a gallon. The calculator handles this for you.

The second mistake is forgetting the second coat. People buy paint for one coat, run out halfway through the second, and rush back to the store. Plan for two coats from the start.

Buying cans from different batches causes color bands on the wall. Always check that all your gallons came from the same mix. When in doubt, box them together.

Skipping surface prep wastes good paint. Wash dirty walls, fill holes, and sand rough spots before you open a can. Paint sticks best to clean, smooth walls, and it looks far better too.

Do not paint in a cold or damp room. Most latex paint wants temperatures above 50 degrees and low humidity. Cold paint gets thick and leaves marks. If you must paint in winter, warm the room first and keep air moving with a fan.

One more tip: stir every can well before you pour. Paint settles in the can, and the color at the bottom is stronger than the color at the top. A good two-minute stir blends it all back together. If you hired a pro, ask them to confirm the gallons before they start so nobody runs short mid-wall.

More Free Home & Garden Tools

Try our other free calculators: Christmas Tree Lights Calculator, Christmas Tree Size Calculator, Rug Size Calculator, Gallery Wall Spacing Calculator, and Raised Bed Soil Calculator. See them all on the Home & Garden Tools page.

Frequently Asked Questions

How much paint for a 12×12 room?

A 12×12 room with 8-foot walls, 1 door, and 2 windows has 333 square feet of wall area. One coat needs 0.95 gallons and two coats need 1.90 gallons. Buy 2 gallons for two coats.

Is one gallon enough for a bedroom?

One gallon covers about 350 square feet with one coat. A small 10×10 bedroom has 269 square feet of wall area, so one gallon covers one coat with some left over. For two coats you need 1.62 gallons, so buy 2 gallons. A larger 12×14 bedroom needs 1.04 gallons for just one coat, so a single gallon is not quite enough.

How much paint for a ceiling?

Multiply the room length by the width. A 12×14 ceiling is 168 square feet. Two coats need 0.96 gallons, so buy 1 gallon of flat ceiling paint. Ceilings usually get their own paint, so the calculator shows the ceiling as a separate result.

Does paint and primer in one mean one coat?

No. Paint and primer in one covers a little better than plain paint, but it is not a true primer. Most rooms still need two coats for even color. On new drywall or over dark colors, use a separate primer first, then two coats of paint.

How much paint do I need for trim and doors?

Trim is figured separately from walls. A good rule is that one quart covers about 90 square feet of trim. Most rooms need 1 to 2 quarts of semi-gloss trim paint. Doors take about half a quart each if you paint both sides.

Should I buy extra paint for touch-ups?

Yes. Buy a little more than the math says, at least a quart extra. Save it in a sealed jar labeled with the room name and the paint color. Touch-ups with the exact same can look invisible. Touch-ups with a new can mixed months later can show.

How do I convert gallons to liters?

Multiply gallons by 3.785. So 2.09 gallons is 7.9 liters, rounded up to 8.0 L. The calculator shows liters when you switch to Meters mode.

What if my room is not a rectangle?

Split it into rectangles and measure each one. An L-shaped room is two rectangles. Add the wall areas together, then enter the total as if it were one room. Or run the calculator once for each section and add up the gallons.