What you need

  • A 25 foot tape measure, or a laser measure. The tape measure guide covers reading the marks.
  • A notepad or graph paper and a pencil.
  • A step ladder for the ceiling, and a second person for long walls if you have one.

With a tape, step by step

  1. Sketch the room from above: every wall, the doors (and which way they swing), windows, closets and anything built in. The guide to reading blueprints shows how plans draw them.
  2. Measure the length along the floor, wall to wall, at the baseboard. Keep the tape straight and tight; a sag on a long wall reads long.
  3. Measure the width the same way, along the wall that meets it.
  4. Measure every jog. In an L-shaped room or one with a bump-out, measure each straight piece of wall and write it on the sketch where it goes.
  5. Measure the ceiling height in a corner, floor to ceiling.
  6. Measure the doors and windows: width and height of each opening, and where it sits along its wall.
  7. Write it as it reads, feet and inches (13’ 7”), and do the math after.

A quick check on a rectangular room: measure both diagonals. If they match, the room is square and length times width is its area.

Turning it into areas

  • Floor area: length × width. A 13’ 7” by 11’ 4” room is 13.58 × 11.33 = 154 square feet. The guide to calculating square footage covers odd shapes.
  • Wall area: the distance around the room × the ceiling height, less the doors and windows. Paint and drywall go by it.
  • Ceiling area: the same as the floor for a flat ceiling.

The square footage calculator adds up rooms and odd shapes in feet and inches.

With a phone

Measuring one wall or object

Apple’s Measure app measures with the camera: point at one end, tap, pan to the other end, tap. Apple says it works best on objects 2 to 10 feet away and calls its measurements approximate. It’s handy for a window or a wall, not for a whole room. The room measurement apps compared covers the apps that do whole rooms.

Measuring the whole room

Floor plan apps measure every wall at once:

  • On an iPhone Pro or iPad Pro, the LiDAR Scanner reads depth, and Apple’s RoomPlan engine turns a walk around the room into a floor plan with every wall’s size, the ceiling height, and the doors and windows.
  • On any other phone, Android included, the app follows the phone with the camera while you mark each corner of the room. The guide to floor plans on Android walks through it.

Either way, the floor area, wall area and ceiling height come out for every room, with the sketch drawn to size. In BluMatrix they go straight into the estimate.

Common questions

How do I figure out the size of my room?

Measure the length and width along the floor and multiply them: a 12 by 10 room is 120 square feet. For an odd-shaped room, split it into rectangles and add them.

How big is a 10 by 12 room?

120 square feet of floor. With 8 foot ceilings it has 2 × (10 + 12) × 8 = 352 square feet of wall.

What is length × width × height?

The room’s volume in cubic feet. A 12 by 12 room with 8 foot ceilings is 1,152 cubic feet. Heating and cooling are sized by it; flooring and paint go by area instead.

Should I measure to the baseboard or the wall?

For flooring, measure at the floor wall to wall; the baseboard sits on top of the flooring’s edge. For a floor plan, measure wall to wall.

Is a laser measure more accurate than a tape?

On long walls, usually, because it can’t sag. Aim it at a flat surface square to the beam.