How to Calculate Square Footage of a Room

Whether you are buying flooring, quoting a paint job, or listing a property, you need to know how to calculate square footage. It is one of the most useful home measurements, and the good news is that it comes down to simple multiplication: length times width. This guide shows you exactly how to measure a room, add up multiple rooms for a whole house, and handle awkward L-shaped spaces by splitting them into rectangles. It also covers converting between square feet and square metres. For any shape beyond a rectangle, our area calculator does the maths for you, but the method below keeps you in control on site.

The square footage formula

Measure the length and width of the space in feet, then multiply them. The result is the area in square feet. If you measure in inches, divide by 12 first to convert to feet, or measure in feet and inches and convert the inches to a decimal (6 inches is 0.5 feet).

A worked example

Suppose a room is 12 feet long and 10 feet wide.

1. Multiply length by width: 12 x 10 = 120.
2. The room is 120 square feet.

In plain English: a 12-by-10 room covers 120 square feet. That single figure is what you would give a flooring supplier or use to estimate paint, tile, or heating needs.

Measuring a whole house

To find the square footage of a whole home, calculate each room separately and add the results. Measure every room’s length and width, multiply to get its square footage, then sum them all. Include hallways and other usable spaces, and decide consistently whether to count areas like garages or unfinished basements, which are often excluded from living-area figures.

Adding room by room is more accurate than trying to measure the whole outline at once, especially in homes that are not simple rectangles.

For any shape

Our area calculator handles rectangles, circles, and triangles, so you can measure unusual rooms easily. Once you have your square footage, our guide on how much flooring you need turns it into materials.

Irregular and L-shaped rooms

Rooms are rarely perfect rectangles. The reliable trick is to divide an irregular space into rectangles, calculate each, and add them together.

For an L-shaped room, split it into two rectangles along the corner of the L. Work out the square footage of each and sum them for the total. A room with a bay or alcove can be handled the same way: measure the main rectangle plus the smaller sections. Break the awkward shape into simple pieces you can multiply.

Square feet and square metres

If you have measurements in metres, or need to convert, remember that area conversions use a squared factor:

So a 30 square metre room is 30 x 10.764, which is about 323 square feet. To go the other way, divide square feet by 10.764. Never use the linear conversion of 3.28 for area.

Frequently asked questions

How do I calculate square footage?

Multiply the length by the width of the space in feet. A room 12 feet by 10 feet is 12 times 10, which equals 120 square feet. If you have measurements in inches, convert them to feet first by dividing by 12. For rooms that are not rectangular, split them into rectangles and add the square footage of each.

How do I calculate the square footage of a whole house?

Measure each room’s length and width, multiply to get its square footage, then add all the rooms together. Include hallways and usable spaces, and be consistent about whether you count garages or unfinished areas. Calculating room by room is more accurate than measuring the whole outline, especially for homes that are not simple rectangles.

How do I find the square footage of an L-shaped room?

Divide the L-shape into two rectangles along the inner corner. Measure and multiply the length and width of each rectangle to get its square footage, then add the two figures together. This divide-and-add method works for any irregular room, including those with alcoves or bays, by breaking it into simple rectangles.

How do I convert square metres to square feet?

Multiply square metres by 10.764 to get square feet, since area uses a squared conversion factor. A 30 square metre room is about 323 square feet. To convert square feet back to square metres, divide by 10.764. Do not use the linear conversion of 3.28, which applies only to length, not area.

Do I include closets and hallways in square footage?

For usable living area, hallways and built-in closets are typically included, since they are part of the interior space. Areas like garages, unfinished basements, and attics are often excluded from living-area figures. The key is to be consistent and clear about what you have counted, especially when comparing or listing property sizes.

The bottom line

To calculate square footage, multiply length by width in feet, so a 12-by-10 room is 120 square feet. For a whole house, measure each room and add them; for L-shaped or irregular rooms, split them into rectangles and sum the pieces. Convert between square metres and square feet with the factor 10.764, never the linear one. For any shape, use our area calculator.

Further reading

For authoritative background on this topic, see Square foot on Wikipedia.