How to Calculate Square Footage (Free Online Tool)

Whether you are buying flooring, paint or carpet, you need to know your square footage before you can order the right amount or compare prices. This guide explains the simple area formula and walks you through the Square Footage Calculator, which finds area from length and width, converts between sq ft and square metres, adds up multiple rooms, and estimates material cost. It is free, runs in your browser, and needs no sign-up.

How square footage is calculated

Square footage is just area, and for a rectangle the formula is:

Area = length x width

Measure both in feet and multiply. A room 12 feet by 10 feet is 12 x 10 = 120 square feet. For metric, 1 square metre equals about 10.764 square feet, so you can convert in either direction. For non-rectangular spaces, split the area into rectangles, calculate each, and add them together. The calculator handles the multiplication, the conversion and the totalling for you.

How to use the Square Footage Calculator

Measure and calculate in a minute:

1. Open the Square Footage Calculator.
2. Enter the length and width of a room or area.
3. Add more rooms to total the whole space.
4. Read the area in square feet and square metres.
5. Optionally enter a price per square foot to estimate material cost.

For L-shaped or irregular rooms, divide the floor plan into rectangles, enter each one, and the tool adds them into a single total.

A worked example

Suppose you are flooring two rooms. The living room is 15 feet by 12 feet and the bedroom is 11 feet by 10 feet.

• Living room: 15 x 12 = 180 sq ft
• Bedroom: 11 x 10 = 110 sq ft
• Total: 290 sq ft, which is about 26.9 square metres

If flooring costs 3.50 dollars per square foot, the material estimate is 290 x 3.50 = 1,015 dollars. Add a 10 percent waste allowance and you would order about 319 sq ft to be safe.

Common unit conversions

Area units convert with fixed factors. Keep these handy:

The calculator converts automatically, but it helps to know flooring is often sold by the square metre even when you measured in feet.

Use cases

Square footage is the starting point for many projects:

• Flooring, tile, carpet and laminate
• Paint coverage for walls (measure wall area, not floor)
• Landscaping, turf and decking
• Real estate listings and rent per square foot
• Comparing the price of materials

For general unit changes beyond area, the Unit Converter is handy, and the Percentage Calculator helps add a waste allowance. Browse more in calculators.

Measuring an L-shaped or irregular room

Few real rooms are perfect rectangles, so the reliable approach is to split an irregular floor plan into rectangles, find the area of each, and add them up. Picture an L-shaped living room. Draw a line that divides the L into two rectangles: say a main section of 16 feet by 12 feet and an alcove of 8 feet by 5 feet.

• Main section: 16 x 12 = 192 sq ft
• Alcove: 8 x 5 = 40 sq ft
• Total: 192 + 40 = 232 sq ft

The same trick handles bay windows, hallways and closets: treat each as its own rectangle and sum the parts. For a triangular nook, use area = (base x height) / 2. If a space has a curved edge, measure a rectangle that just contains it for a slightly generous estimate, which is safer than coming up short on materials. The calculator lets you enter each rectangle as a separate room and totals them automatically, so you only have to do the splitting on paper.

Estimating material cost and waste

Once you know your area, estimating cost is one more multiplication, but the number you actually order should be higher than your measured area. Flooring and tile come with offcuts, breakages and pattern matching, so trade practice is to add a waste allowance: about 5 percent for a simple square room, 10 percent for a room with many corners or a diagonal layout, and up to 15 percent for patterned tile or herringbone. Suppose a room measures 240 sq ft and the flooring costs 4 dollars per square foot.

Always round up to whole boxes or rolls, since suppliers rarely sell partial units, and keep a spare box for future repairs. Enter the price per square foot in the calculator to get the base cost, then apply your waste percentage on top.

Walls, ceilings and paint coverage

Painting needs wall area, not floor area, which is a common mix-up. To find a wall, multiply its height by its width, add up all four walls, then subtract the area of doors and large windows. For a room 12 feet by 10 feet with 8-foot ceilings, the two longer walls are 12 x 8 = 96 sq ft each and the two shorter walls are 10 x 8 = 80 sq ft each, totalling 352 sq ft. Subtract roughly 21 sq ft for a standard door and 15 sq ft for a window, leaving about 316 sq ft to paint. Compare that to coverage on the paint tin, often around 350 to 400 sq ft per gallon for one coat, so one gallon covers a single coat and you would buy two gallons for two coats. The ceiling is simply the floor area, 120 sq ft here. Measuring walls and ceiling separately stops you from under-buying paint, the most frequent mistake on a decorating project.

Tips and privacy

Measure accurately with these tips:

• Always add a waste allowance, usually 5 to 10 percent, for cuts and mistakes.
• Measure twice; a small error is multiplied across the whole area.
• For walls, measure height by width and subtract doors and windows.

The Square Footage Calculator runs entirely in your browser, so your measurements are never uploaded or stored. It is free with no sign-up. Keep the Square Footage Calculator open while you plan. See all tools for more.