Paint Calculator

Created by Gabriela Diaz
Last updated: Jul 07, 2022

This interior paint calculator will simplify your paint or renovation projects 🏡 Wondering how much paint do I need? Use this tool to calculate the painting area, amount of paint needed, and calculate paint cost.

Keep reading to learn:

  • How to estimate the painting area;
  • How to calculate the amount of paint needed; and
  • How to calculate paint cost.

Estimate paint needed — How much paint do I need?

Let's look at how to estimate the amount of paint you'll need to cover the walls of a room and some factors to consider:

1. Determine the area of the room

To begin our calculation, we'll determine the total surface area that will be painted. To do this, measure the length, width, and height of the room and determine the surface area of the room with the following formula:

Room Surface Area=Length×Width×Height\footnotesize \text{Room Surface Area} = \text{Length} \times \text{Width} \times \text{Height}

Subtract the surfaces that will not be painted. This usually refers to doors and windows or any other openings:

Openings Area=N° Openings×Length×Height=Doors Area+Windows AreaNet Room Area=Room Surface AreaOpenings Area\footnotesize \begin{aligned} \text{Openings Area} &= \text{N° Openings} \times \text{Length} \times \text{Height} \\ &= \text{Doors Area} + \text{Windows Area} \\ \text{Net Room Area} &= \text{Room Surface Area} - \text{Openings Area} \end{aligned}

This last result represents the room's square footage or total area that will be painted.

Finding the area of a room is similar to determining the area of a rectangle. Take a look at our area of a rectangle calculator to learn more 🟪

2. Calculate the amount of paint

Now that we've estimated the overall room area, we can estimate how much paint we'll need to cover this space. For this, we need to know the paint efficiency or coverage factor, which is the area that can be covered per liter or gallon of paint. Usually, you can find this number on the can of paint in m2/l or ft2/l. If it is not a hand, an estimated value of 350 square feet per gallon of paint might be used.

Another consideration is the number of coats that will be applied. This depends on factors such as if we're painting over the same or similar color, in which case one coat should suffice, whereas going from dark to light may require two or three coats. Also, you can consider how pigmented and how thin the paint is.

You can use this formula to calculate the paint needed:

Paint Amount=Net Room Area×Paint Eff.×N° Coats\footnotesize \text{Paint Amount} = \text{Net Room Area} \times \text{Paint Eff.} \times \text{N° Coats}

The amount of paint required is also affected by the wall's texture; for example, porous surfaces require more paint than smooth surfaces, consider including extra paint when working with irregular surfaces.

3. Estimate the cost of paint

Finally, to better understand the budget needed to complete your painting project, let's look at how to calculate the paint cost. To do this, multiply the amount of paint we calculated in the previous step by the cost per gallon or liter:

Paint Cost=Paint Amount×Unitary Cost\footnotesize \text{Paint Cost} = \text{Paint Amount} \times \text{Unitary Cost}

💡 Please keep in mind that the results of these calculations are estimates. Different factors are present; paint can vary from brand to brand, and thinner or less pigmented paints may require more product than thicker and/or more pigmented paints.

We have many other tools that can help you plan your decoration and renovation projects, like the tile calculator and the brick calculator 🧱

How to use the interior paint calculator

You can easily estimate the amount of paint required to cover the surface of a room using the interior paint calculator; just keep the following steps in mind:

  1. Begin by inputting the room's dimensions to determine the total wall area. Enter the values of Room length, Room width, and Room height  into the calculator's appropriate fields.

  2. By considering openings or areas of doors and windows, you may exclude surfaces that won't be painted.

  3. To exclude the area of the doors, enter the Number of doors that will not be painted. Notice that the calculator will show standardized door dimensions, but you can modify them to meet your specific measurements.

  4. Similarly, to discard the windows' area from the total area, enter the Number of windows and their dimensions.

  5. Once done with the inputs, the calculator will display the results in the Amount of paint section. Here you can find the Net room area, Amount of paint, and Total cost required to paint the particular room. You can modify other settings such as the Number of coats and Paint efficiency, which will affect the total amount of paint and costs.

🙋 This paint calculator does not include the ceiling in the calculations. If you plan to include it, you'll need extra paint.

Gabriela Diaz
Room length
ft
Room width
ft
Room height
ft
Room surface area
ft²
Doors
Door height
in
Door width
in
Number of doors
Total doors area
ft²
Windows
Windows height
in
Windows width
in
Number of windows
Total windows area
ft²
Amount of paint
Net room area
ft²
Number of coats
Paint efficiency
ft²
/l
Amount of paint
US gal
Cost per unit
$/
US gal
Total cost
$
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