How to Calculate How Much Paint You Need

When embarking on a paint project, the last thing you want is to spend too much or too little on the paint you need. Buy too little and you're interrupting your project to run back to the store. Buy too much and you're stuck with cans that you can't safely dispose of.

Before rolling up the sleeves, make sure you know how to calculate how much paint you'll need. For precise measurement, a paint calculator will help you figure out how much paint is necessary for your exact room. Alternatively, if you'd rather not make calculations, you can purchase paint quantities based on a few basic room types, such as for small bedrooms, powder rooms, medium kitchens, or large/suite bedrooms.

How to Precisely Calculate Square Footage for Painting

To precisely calculate how much paint to purchase, add the wall and ceiling spaces (area), then add wastage but subtract the cutouts.

Plan to have enough paint for two coats of paint. Take the square footage of the ceiling into the calculation if you'd like to include it in your paint project. Painting projects for entire rooms are based on a wall coverage factor of 350 to 400 square feet per gallon of paint.

• Add Walls: The square footage, or area, of a wall is determined by multiplying the width of the wall by the height of the wall. The area of each wall should be calculated individually. After all wall areas are determined, these figures are added together.
• Add Ceiling: Ceiling square footage is calculated by multiplying the width of one wall by the width of an adjacent wall. No exclusions are made for ceiling elements such as light fixtures or smoke alarms.
• Add Wastage: Multiply 10- or 15-percent (0.10 or 0.15) into the combined walls and ceiling area to arrive at the wastage amount. Add this wastage amount to the total. Wastage accounts for spills and evaporation.
• Subtract Cutouts: Anything that does not get painted is a cutout. The combined area of cutouts should be subtracted from the total paint calculated for the walls, ceiling, and wastage.

How to Quickly Calculate Paint Quantities

Is there a faster way to calculate paint quantities? Yes, there is. Omit two steps: subtracting the non-paintable areas and adding in wastage. Itemizing all of the cutouts can be a painstaking process. Eliminating that step makes the process easier. The 10- to 15-percent wastage amount will replace the cutout subtractions.

If you're unsure of exactly how much paint you need, we included some average estimates below. Aim to buy an extra gallon of paint in the event that you need extra, and also for future touch-ups.

How Much Paint to Use for Bathrooms

How Much Paint to Use for a Powder Room

• Floor Size: 20 square feet
• Wall Space: 124 square feet
• Use: 1 gallon of paint

Because they have no bathtub or shower, powder rooms walls are usually in such good condition that two coats with one gallon of paint is sufficient. This sample calculation excludes 20 square feet for one entry door from the total wall space. Powder rooms tend not to have windows.

How Much Paint to Use for a Small Bathroom

• Floor Size: 40 square feet
• Wall Space: 108 square feet
• Use: 1 gallon of paint

For a small bathroom with minimal wall problems, you can usually purchase just one gallon of paint. This calculation excludes one entry door, one window, and 65 square feet of wall space for a bathtub and surround.

How Much Paint to Use for a Medium Bathroom

• Floor Size: 120 square feet
• Wall Space: 252 square feet
• Use: 2 gallons of paint

For this bathroom calculation, excluded are both a window and an entry door, along with 65 square feet for the tub/surround.

How Much Paint to Use for a Large Bathroom

• Floor Size: 160 square feet
• Wall Space: 316 square feet
• Use: 2 gallons of paint

For this large bathroom, two gallons of paint will comfortably cover all wall areas with a little paint to spare. This calculation excludes both a window and an entry door from the total wall space. An alcove tub and surround calculated at 65 square feet of wall space are excluded, as well.

How Much Paint to Use for Kitchens

Kitchens are heavy-use areas, so they always require a thorough paint job. At the same time, kitchens tend to have limited wall space due to the base and wall cabinets, reducing the amount of paint you will need. Buy quality paint in eggshell or semi-gloss sheens for easier kitchen cleanup.

How Much Paint to Use for a Small Kitchen

• Floor Size: 100 square feet
• Wall Space: 243 square feet
• Use: 2 gallons of paint

Plan on purchasing two gallons of paint for all types of small kitchens. One door, one window, and 42 square feet of base and wall cabinets are excluded from the wall space square footage.

How Much Paint to Use for a Medium Kitchen

• Floor Size: 200 square feet
• Wall Space: 383 square feet
• Use: 2 gallons of paint

Use two gallons of paint for two coats of paint in average-sized kitchens. One door, one window, and 62 square feet of base and wall cabinet space are excluded to produce the total wall space.

How Much Paint to Use for a Large Kitchen

• Floor Size: 300 square feet
• Wall Space: 515 square feet
• Use: 3 gallons of paint

The sample net calculation of paint for a large kitchen excludes two windows and one door from the total wall space, along with 75 square feet of base and wall cabinet space.

How Much Paint to Use for Bedrooms

Bedrooms tend to use more paint than other areas of the home. Though walls are usually in good condition and rarely require more than two coats of paint, there usually is a lot of wall space. That's because most bedrooms have few built-in obstructions.

How Much Paint to Use for a Small Bedroom

• Floor Size: 150 square feet
• Wall Space: 345 square feet
• Use: 2 gallons of paint

The sample net calculation excludes both a window and two doors from the total wall space. One door is the entry door. The other door is a single-width closet door occupying 20 square feet of unpainted wall space.

How Much Paint to Use for a Medium Bedroom

• Floor Size: 200 square feet
• Wall Space: 405 square feet
• Use: 3 gallons of paint

Medium-sized bedrooms will use about three gallons of paint. With this calculation, one window and three doors are excluded. One of those doors is an entry door. The other two doors account for a double-width closet door that uses 40 square feet of unpainted wall space.

How Much Paint to Use for a Large Bedroom

• Floor Size: 300 square feet
• Wall Space: 565 square feet
• Use: 4 gallons of paint

With this large primary bedroom calculation, excluded are one entry door, one window, and two additional doors to account for a double-width closet occupying 40 square feet of unpainted wall space.