How to measure a room for furniture

A step-by-step method for measuring a room so your plan matches reality: walls, diagonals, doors, windows and the fixed things people forget.

A floor plan is only as good as the numbers behind it. Ten careful minutes with a tape measure prevents most “it doesn’t fit” surprises. This guide gives you a routine that works for any room and tells you which numbers to type into the Room Planner.

What you need

A steel tape measure of at least 5 m (16 ft). Cloth tapes stretch.
Paper and pencil, or your phone’s notes.
A second person for long walls, if possible.

Step by step

Sketch the room first. Draw a rough outline, not to scale, and mark every door, window, radiator, column and built-in cupboard. You will write measurements onto this sketch.
Measure each wall at floor level, from corner to corner. Skirting boards (baseboards) take up space that furniture feet need, so measure between skirting boards if furniture will stand against the wall.
Measure each wall again about 1 m (3 ft) up. Walls lean and bulge. If the two numbers differ, plan with the smaller one.
Measure both diagonals. In a truly rectangular room the two diagonals are equal. If they differ by more than a centimetre or two, the corners are not square and large items may not sit flush in a corner.
Locate every door. Note the distance from the nearest corner to the edge of the opening, the clear width of the opening, which side the hinges are on and which way the door swings.
Locate windows and fixed objects. Record distance from a corner, width, and how far each radiator, pipe, column or fireplace sticks out from the wall. Note sill heights if furniture will stand under a window.
Measure the ceiling height in at least two places, and under any beams or sloped sections.

Measure every wall twice, both diagonals, and each door’s distance from a corner.

Worked example

Wall A measures 402 cm at floor level and 400 cm at 1 m. Wall B measures 300 cm both times. Use 400 × 300 cm. For a perfect rectangle of that size each diagonal would be 500 cm (because 300² + 400² = 500²). You measure 500 cm and 494 cm. The 6 cm difference tells you one corner is noticeably out of square, so a wardrobe pushed into that corner may leave a wedge-shaped gap. Plan a few centimetres of tolerance there.

Rooms that are not rectangles

The planner supports L-shaped, U-shaped and T-shaped rooms, a room with one angled corner, and round or oval rooms. Measure the overall width and depth first, then the size of the part that is “missing”. For anything more unusual, use the closest shape and place a “Fixed obstacle / unusable area” item over the space you cannot use.

Common mistakes

Measuring wall to wall above the skirting board, then finding the furniture is 3 cm too wide at floor level.
Forgetting the radiator, which can stand 10 cm or more off the wall.
Recording the door’s frame width instead of the clear opening.
Rounding up. Always round room sizes down and furniture sizes up.

Limits of a plan

A plan shows the floor only. Sloped ceilings, low window sills, sockets, switches and vents do not appear in the planner; keep them on your paper sketch and check them yourself.

Enter your measurements in the Room Planner

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