How do I calculate square footage?

Multiply length by width in feet. A 12 ft by 15 ft room is 12 × 15 = 180 square feet. For an odd shape, split it into rectangles and triangles, work out each one, and add them up. Subtract any notch or cutout that isn't part of the floor.

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

Split the L into two rectangles that don't overlap, multiply length by width for each, and add them. For a 30 × 24 ft block with a 14 × 12 ft wing, that's 720 + 168 = 888 square feet. Or measure the full bounding rectangle and subtract the missing corner.

How do I convert inches to feet for square footage?

Divide the inches by 12 before you multiply. 11 ft 6 in is 11.5 ft, 10 ft 3 in is 10.25 ft and 9 ft 9 in is 9.75 ft. A room 12 ft by 11 ft 6 in is 12 × 11.5 = 138 square feet. This calculator accepts feet and inches directly, like 11' 6".

How many square feet are in a square yard and a square meter?

A square yard is 9 square feet, because a yard is 3 feet and 3 × 3 = 9. A square meter is about 10.764 square feet, and one square foot is 0.0929 square meters. Carpet is usually priced by the square yard, and plans drawn in metric give areas in square meters.

Should I measure inside or outside the walls?

It depends on what the number is for. Flooring, paint and room sizes use inside dimensions, wall face to wall face. A home's total square footage for a listing or appraisal is measured around the outside of the exterior walls, level by level, which is why room sizes add up to less than the house total.

Free calculator

Square Footage Calculator for Rooms and Houses

Free square footage calculator. Add rooms, L-shapes and triangles in feet and inches and get square feet, square meters and square yards.

Shapes

Shape
Add or subtract
Length
ft
Width
ft
Shape
Add or subtract
Length
ft
Width
ft
Shape
Add or subtract
Base
ft
Height
ft

Feet, or feet and inches: 12, 12.5, 12' 6". A triangle is base × height ÷ 2, where the height is measured square to the base.

Result

Total area

870sq ft

Square meters: 80.8 m²
Square yards: 96.7 sq yd

By shape

Main block (rectangle)+720.0 sq ft
Wing (rectangle)+168.0 sq ft
Angled corner (triangle)−18.0 sq ft

Rectangles that touch but don't overlap can simply be added. Subtract notches, clipped corners and anything that doesn't count.

How it's calculated

Square footage = length × width for each rectangle, plus base × height ÷ 2 for each triangle, minus any cutouts. A 30 × 24 ft block (720 sq ft) plus a 14 × 12 ft wing (168 sq ft), less a clipped corner of 6 × 6 ÷ 2 (18 sq ft), is 870 sq ft.

How to use the square footage calculator

Break the floor into simple shapes. Each row is a rectangle (length × width) or a right triangle (base × height ÷ 2). Set a row to Subtract for anything that comes out of the floor: a notch, a clipped corner, a two-story opening or a chimney chase. Lengths can be feet (12.5) or feet and inches (12' 6"). The total updates as you type, in square feet, square meters and square yards.

There are two ways to handle an L-shaped room. Add two rectangles that only touch, or take the full bounding rectangle and subtract the missing corner. Both give the same answer. Just don't let added shapes overlap, or the overlap is counted twice.

Area formulas for common shapes

Shape	Formula	Example
Rectangle or square	length × width	14 × 12 = 168 sq ft
Right triangle	base × height ÷ 2	6 × 6 ÷ 2 = 18 sq ft
Any triangle	base × height ÷ 2 (height square to the base)	10 × 4 ÷ 2 = 20 sq ft
L-shape	two rectangles added	720 + 168 = 888 sq ft
Room with a notch	bounding rectangle − notch	(16 × 14) − (4 × 3) = 212 sq ft
Angled bay	rectangle + two triangles	(8 × 2) + 2 × (2 × 2 ÷ 2) = 20 sq ft

For a wall at an angle, draw a line square to the other walls where the angle starts. That splits the floor into a rectangle and a right triangle, and the triangle's base and height are the two straight distances you can measure with a tape. The guide to irregular rooms walks through more shapes.

A worked example

The calculator opens with this floor: a main block, a wing and a clipped corner.

Shape	Math	Area
Main block	30 × 24	+720 sq ft
Wing	14 × 12	+168 sq ft
Angled corner (triangle)	6 × 6 ÷ 2	−18 sq ft
Total	720 + 168 − 18	870 sq ft
In square meters	870 × 0.0929	80.8 m²
In square yards	870 ÷ 9	96.7 sq yd

Unit conversions

From	To	Multiply by
Square feet	Square meters	0.0929
Square meters	Square feet	10.764
Square feet	Square yards	÷ 9
Square yards	Square feet	9
Inches	Feet	÷ 12 (6 in = 0.5 ft, 9 in = 0.75 ft)

Room sizes vs. a home's square footage

Adding up room sizes gives you the floor area inside the walls, which is what you need for flooring, paint and furniture. It won't match a home's listed square footage. Listings and appraisals measure around the outside of the house, include halls, closets and the walls themselves, and leave out garages and below-grade space. For that number, use the GLA calculator or read how to measure a house's square footage.

If you have a floor plan, you don't need to split shapes by hand. FloorFigures is free: open the PDF or image, set the scale, click inside each room, and it traces the walls and adds up the area for you, with overlaps counted once.

Updated October 12, 2026 · FloorFigures

Questions

How do I calculate square footage?: Multiply length by width in feet. A 12 ft by 15 ft room is 12 × 15 = 180 square feet. For an odd shape, split it into rectangles and triangles, work out each one, and add them up. Subtract any notch or cutout that isn't part of the floor.
How do I calculate the square footage of an L-shaped room?: Split the L into two rectangles that don't overlap, multiply length by width for each, and add them. For a 30 × 24 ft block with a 14 × 12 ft wing, that's 720 + 168 = 888 square feet. Or measure the full bounding rectangle and subtract the missing corner.
How do I convert inches to feet for square footage?: Divide the inches by 12 before you multiply. 11 ft 6 in is 11.5 ft, 10 ft 3 in is 10.25 ft and 9 ft 9 in is 9.75 ft. A room 12 ft by 11 ft 6 in is 12 × 11.5 = 138 square feet. This calculator accepts feet and inches directly, like 11' 6".
How many square feet are in a square yard and a square meter?: A square yard is 9 square feet, because a yard is 3 feet and 3 × 3 = 9. A square meter is about 10.764 square feet, and one square foot is 0.0929 square meters. Carpet is usually priced by the square yard, and plans drawn in metric give areas in square meters.
Should I measure inside or outside the walls?: It depends on what the number is for. Flooring, paint and room sizes use inside dimensions, wall face to wall face. A home's total square footage for a listing or appraisal is measured around the outside of the exterior walls, level by level, which is why room sizes add up to less than the house total.

Skip the typing. Measure the plan.

Open the floor plan in FloorFigures and every room is measured for you, with the same math per room. Try it free on a sample plan; nothing is uploaded.