How to Measure Square Footage: Room by Room, Then Add It Up

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Rooms that are not rectangles are split into rectangles first. Type the numbers into the calculator below to add them up, or draw the rooms on the canvas and the area is worked out from the walls, so the measurements end up on a plan you can send to an agent, a contractor or a buyer. This is a measuring guide and a 2D drawing tool, not an AI estimate.

01

Three ways to measure a room

A tape measure is the baseline: hook it on one wall, pull it straight to the opposite wall at floor level, and read the number where the tape meets the wall, not the baseboard. Measure twice if the tape sagged. A laser measure is faster and better for long rooms: hold it flat against one wall, aim at the opposite wall and read the display; most are accurate to about 1/16 inch over 30 feet. Phone apps that scan a room are quick for a rough number but drift in large or cluttered spaces, so use them for a first pass and confirm the key walls with a tape or laser.

Whichever tool you use, measure every room the same way: inside face of wall to inside face of wall, at floor level, along the longest straight line. Write length and width as you go. Note doors, closets and anything that sticks into the room, like a chimney breast or a column.

02

Odd shapes: split them into rectangles

An L-shaped room is two rectangles. A room with an alcove or a bay is a main rectangle plus a small one. Measure each rectangle on its own and add the areas; the calculator above has a row for each section. For a sloped ceiling, only the floor under a usable ceiling height counts in most listing standards, usually 5 feet or more, with at least half the area at 7 feet. Closets inside a room are usually counted with it.

If a room has a diagonal wall or a curve, measure the bounding rectangle and subtract the missing triangle, or simply draw the shape on the canvas: click each corner, type the lengths, and the area of any closed shape is worked out exactly.

• L-shape: two rectangles, added.
• Bay window or alcove: main rectangle plus the alcove, if it is floor to ceiling.
• Under a slope: count only the floor with usable height.
• Curved or angled walls: draw it, the canvas does the geometry.

03

Measuring a whole house

For a total, listing standards in the United States (ANSI Z765) measure the outside of the house, floor by floor, and include only finished living space with a ceiling of at least 7 feet, heated and directly accessible from the rest of the house. Garages, unfinished basements, open porches and attics without stairs are listed separately. Room-by-room inside measurements come out a little smaller than the exterior method because the walls are not counted; say which method you used when you share the number.

For a renovation or a materials order, the inside measurements are the ones you want: flooring, baseboards, paint and drywall are bought for the rooms, not the footprint.

04

Put the numbers on a plan

Once each room is measured, draw it: start at a corner, type the wall length, turn, type the next. Rooms close and show their area; switch on "Wall lengths" and every wall carries its measurement. The free image export has the dimensions and areas on it, and the paid PDF prints to a standard scale. The plan is schematic, not a survey or an appraisal, and it is not an AI tool that guesses sizes from a photo.