How Much Paint Do I Need? A Paint Calculator to Paint Like a Pro

It is difficult to predict how much paint to buy, and a paint calculator is a helpful resource. Paint calculators allow you to budget the amount of money you need to spend for your project in advance.

How Much Paint Do I Need

Also, paint calculators give you the ability to buy the right amount so that you aren’t wasting money on paint you don’t need.  

how much paint to buy
Aneta Lusina

How Much Paint Do I Need?

The amount of paint you need depends on a couple of factors including the size of the room, texture of the wall, color and type of VOc paint.

We will show you how to calculate these numbers by hand and link to a paint calculator where you can double-check your numbers.

Paint Coverage by Size

  • Quart – 100 square feet
  • One Gallon – 350-400 square feet
  • Five Gallons – 1750-2000 square feet
Paint Coverage by Size
Aneta Lusina

Size of the Room or Surface

The most important factor in determining how much paint you need is the size of your room or the surface you are painting.

Painting the Walls

  1. First, measure the distance or perimeter around the room in total feet.
  2. Next, multiply this number by the height of the walls up to the ceiling.
  3. Then, calculate the area of the windows and doors and subtract this from the total square footage to get your final number.


  1. We are beginning with a room that measures 10 feet on two walls and 12 feet on two walls. If we add 10 + 12 = 22 and then multiply this total number by 2, we get 44 feet.
  2. Next, we multiply this number by the height of the walls up to the ceiling which is 8 feet high. Therefore, our numbers look like this 44 ft x 8 ft = 352 square feet.
  3. Then, you need to subtract the square footage from the number of doors and windows you have in the room. We will calculate one door and two windows in this room. The square footage of our door is 21 sq. feet and the two windows are each 15 square feet each (15 sq. ft. x 2 = 30 sq. ft.). We add these together and then subtract 51 square feet from our total square footage. 352 sq. ft.- 51 sq. ft.  = 301 square feet.
  4. Therefore, since a gallon of paint covers around 300-400 square feet, you need one gallon of paint for one coat in this room. If you are painting more than one room the same color, calculate all the square footage together.

Painting the Ceiling

Calculate the total square footage of the ceiling by measuring the length x width and multiplying it by 2.

Therefore, if the ceiling measures 10 x 12, then the total square footage of the ceiling is 120 sq. feet. The paint needed for the ceiling for a first and second coat is one gallon.

Painting Trim

Calculate for the amount of trim by measuring the perimeter of the room. To determine the correct baseboard amount, make sure to calculate the height of the baseboard in the calculation.

The same is true of crown molding. If you are determining the amount of paint needed for windows and doors, determine the area of each and add to the total square footage for trim.


We will calculate this number using the previous room example that is 10 x 12 feet to find the amount of paint we need for the trim. 

  1. The perimeter of the room is equal to 44 feet. 
  2. Next, we calculate this for our 6 inch baseboard around the room. 
  3. We need to subtract 3 feet for the one door opening in the room. Our equation is 44 ft. – 3 ft.= 41 feet. 41 ft x .5 ft (6 inches) = 20.5 square feet.
  4. If we have 4 inch crown molding around the room, our calculation looks like this: 44 ft x .3 ft = 13.2 square feet. 
  5. If we add the total square feet of the trim (including the former windows and door), it is 20.5 sq. ft. + 13.2 sq. ft. + 21 sq. ft. + 30 sq. ft. + = 84.7 square feet. One quart, which covers 100 square feet, is enough for the trim in the room.

Color of the Paint

Color of the Paint
Miguel Marmolejos Fernández

The actual paint colors you buy affect how much paint you use. For example, if you are changing your room color from a light shade to a dark shade, you need to paint at least two coats of paint in order to get the saturated color that you want. 

Dark colors require more coats of paint. Likewise, if you are painting a dark room a light color, you need more coats of paint.

If you are painting a light-colored room a similar or same color, you often use just one coat of paint.

Type of Paint

Type of Paint

There are certain kinds of paints that can reduce the number of coats that you use.

For example, there are new paint formulations called “one-coat paints“.

These are combinations of paint and primer. Depending on the surface you are painting, the one coat formulation is not a guarantee.

Surface Type

Surface Type
Miodrag Kitanović

Different surfaces may require more or less paint than others. For example, rough surfaces like concrete or textured walls will need more paint than surfaces that have a glossy finish.

In addition, surfaces that have never been painted will soak in more paint. Therefore, you will need to account for this when you calculate the amount of paint you will need.

In contrast, surfaces that have been painted will not require as much paint. Therefore, the amount you need will be around the amount that you calculate using the hand method or with a paint estimator.

Application Method

Application Method
Delcea Nicolae Cosmin

The method you use to apply the paint will determine the amount of paint you will use. For example, using a sprayer for your interior or exterior will use more paint than hand brushing.

When you spray paint, the sprayer will sometimes overspray and you will waste paint when you have to empty the sprayer.

Paint Calculators

Many paint companies feature a paint calculator to help you or your contractor before you buy paint.

Sherwin Williams Paint Calculator – This handy paint estimator from Sherwin Williams provides several options: a quick calculator, a custom calculator, and a calculator for decks.

Benjamin Moore Paint Calculator – This paint estimator is clear and easy to use.

Behr Paint Calculator – This paint calculator features some levels of customization that make it a useful tool to get a rough estimate of the paint you need.

Frequently Asked Questions (FAQ)FAQ

How many gallons of paint do I need?

The number of gallons you need is dependent on the square footage of your room. Each gallon of paint will cover between 350 and 400 square feet. If you calculate that your room is 486 square feet, you will need 2-3 gallons depending on how many coats of paint you will need. The number of coats of paint is dependent on the actual paint colors, the surface types, and the application method you will use.

How much paint per square foot?

Each gallon of paint is different, and you should look at specific manufacturers to see their coverage charts. However, in general, each gallon of paint will cover around 350-400 square feet.

How much paint do I need for one wall?

The amount of paint you need depends on the size of the wall. For example if you wall is 12 wide and 9 feet high, multiply these numbers together to determine the square footage of the entire wall. This would look like this: 12 x 9 = 108 square feet. Therefore, you will need just one gallon for a wall of this size for one coat or two coats of paint.

How much does it cost to paint a room 12x12?

The cost of painting a room is determined by how much paint you need as well as the cost of each gallon of paint. First, we need to calculate. the square footage of the room. This room is 12 x 12 with 8 foot ceilings. This room has 384 square feet (not including windows and doors). If we know that we will use around 2 gallons for two coats in this room. If the average cost of paint is between $15-$60 a gallon, the cost will be between $30- $120 for the whole room, depending on the kind of paint we choose.


It is important to get a rough idea of how much paint you need to buy before you purchase your paint.

Using a paint calculator and applying the tips above are important tools to help you do just that.

One of the most important parts of a good job is to plan well. If you do that, you will be able to spend your time creating beauty rather than worry about wasting extra resources.