How Much Paint Do I Need for My Walls? Here’s an Easy Way to Find Out
Use this simple math to get to the fun part quicker
Highlights
One gallon can of paint covers up to 400 square feet.
You can multiply the length by the height of each wall to get your room’s square footage.
Don’t forget to subtract the square footage of trim, windows, and doors in your measurements.
A 300-square-foot room with a window will need an average of 1.5 gallons for two coats of paint.
If you want to give your space a facelift, painting your rooms is an easy, DIY-friendly way to totally transform your home. But once you have that perfect shade picked out, you’ll probably run into the question that most of us have asked ourselves at this point: “How much paint do I need?” With a little bit of math, you can figure out exactly what you need and avoid having to dispose of leftover paint.
How Many Gallons of Paint Do I Need per Square Foot?
While some paint formulas and wall textures may require more specific amounts, here are some basic numbers to keep in mind about paint coverage by the gallon:
One gallon of paint can cover up to 400 square feet. This is enough to cover a small room, like a bathroom.
Two gallons of paint can cover up to 800 square feet, enough to cover an average-sized room in two coats of paint.
Three gallons of paint can cover up to 1,200 square feet, enough to cover a couple of average-sized rooms or one large room.
Four gallons of paint can cover up to 1,600 square feet, enough to cover several average-sized rooms.
How Much Primer Will I Need?
Primer actually covers less area than paint does, at about 200 to 300 square feet per gallon. For a small room of 400 square feet, you’d need 2 gallons of primer. A good rule of thumb is to divide the total square footage of what you’re painting by 200 to know how much primer you need to buy.
For example, if you’re priming a 144-square-foot room, you’ll divide 144 by 200. This leaves you with .72 gallons, meaning you'd be safe buying just 1 gallon of primer.
How to Calculate How Much Paint You Need
To calculate the square footage of solid walls:
Measure the length of all walls from corner to corner.
Measure the room’s height from floor to ceiling, minus any trim, baseboards, and crown molding.
Multiply the walls’ lengths by the height; the number you get is the room’s square footage.
For example, say you have a room with a solid wall that measures 10-by-10 feet (100 square feet) and a second solid wall of 12-by-10 feet (120 square feet). The two solid walls together would be 220 square feet.
Calculating Walls With Doors and Windows
To calculate the square footage of a wall with a door or a window:
Measure the length and height of a wall to find its total square footage.
Measure the door/window area, including the window frame and glass, and leave out any molding. Typically, doors are 21 square feet, and most windows are 15 square feet on average.
Subtract the area of each door/window from the total wall area.
As an example, if you have a 12-by-10-foot wall (120 square feet) with one 4-by-6-foot window (24 square feet), you should subtract 24 from 120, leaving you with 96 square feet of wall to paint.
Calculating Ceilings
Whether you’re using the same color or a different color than the walls when painting the ceiling, here’s the process you should follow to measure the square footage:
Measure the length and width of the room’s ceiling.
Multiply the measurements to find the square footage.
If you’re using the same color, treat the ceiling as a fifth wall. If you’re using a different color, estimate the square footage and multiply by two to account for a second coat.
Calculating Rooms With Trim or Molding
If you’re painting your trim or molding a different color than the walls:
Measure the length and width of each trim, crown molding, window, and door frame separately from the rest of the room.
Multiply the length by the width to get the square footage of the area you’ll be painting.
Double-check your calculation using HomeAdvisor’s paint calculator.
How Much Paint Should You Buy?
Divide the total square footage by the approximate coverage of your chosen paint (usually 400 square feet per gallon, but your container will have an exact number). This math will tell you how many gallons of paint you’ll need for one coat.
Multiply this number by two to estimate how much paint per square foot you’ll need in order to give the walls two coats, which pros usually recommend. Round up uneven numbers and purchase slightly more paint for waste allowance, but not so much as to have to throw the paint away. Doing so will keep you from making multiple trips to the home improvement store for more paint and save you some paint for future touch-ups.
DIY vs. Hiring a Pro
Painting is one area in home projects where you can save quite a bit of money by choosing to make it a DIY project versus hiring a professional. The cost of hiring a professional averages $1,100 for a standard-sized room. However, if you choose to paint the room yourself, the average cost drops to around $150 for materials.
While painting a room yourself can save a significant amount of money, it does take considerable time. A local painter has more tools for accurate prepping and painting and has the experience to work at a more efficient pace, so you’ll have to decide which route is better for your schedule and wallet.
Marwa Hasan contributed to this article.
Frequently Asked Questions
The average wall height for a room is 8 feet. If each wall is also 12 feet across, multiply 8 by 12 and multiply that total by 4 (since you most likely have four walls in your room). This comes out to 384 square feet.
Next, divide 384 by 400 since a gallon of paint can usually cover 400 square feet. That number is .96, so you can buy 1 gallon of paint for a 12-by-12 room with 8-foot-tall walls. However, if you’re adding a second coat, multiply that number by two and buy 2 gallons of paint.
Yes. Two gallons of paint will work for any room up to 800 square feet if you’re applying a single coat since 1 gallon of paint can typically cover about 400 square feet. If you’re adding multiple coats or want to paint the ceilings as well, you’ll need to take these measurements into account and grab more paint before you start your project.
The number of coats you need will differ based on a lot of factors. Typically, professionals recommend two coats of paint for maximum, even coverage. However, if you’re on a tight budget and going from a lighter to a darker paint color, you may be able to get away with just one coat.
If you’re going from a darker to a lighter color, like white to black, you may need up to three coats. Buying high-quality paint and using primer on the walls beforehand can save you the extra labor and cost that comes with adding more coats of paint.