How to Measure a Room
Measuring in a fixed order catches a missed alcove or a window measured from the wrong corner before either reaches your plan. The order below shows how to measure a room on your own or with a helper: sketch, wall lengths, both diagonals, openings, then heights. You need a tape or laser measure, paper and a pencil, and about fifteen minutes per room.
What to measure
Why the order matters
Measuring in a fixed order means nothing gets skipped and every number has a place on the sketch. Wall lengths give the shape, but four lengths fit many shapes: a rectangle and a slightly skewed one can have the same sides. The two diagonals settle which one you have. Openings come next because they are measured from the corners you have fixed, and heights last because they matter less for the plan itself.
Measure the inside faces of the walls, at the same height each time. Skirting boards (baseboards), radiators and bulging plaster all shift a reading by a centimetre or two, so pick one height above the skirting and stick to it.
Measuring a room step by step
Sketch the room first
Draw the outline freehand with every wall, door, window and recess. Letter the walls A, B, C… so each number has a home.
Measure each wall
Measure corner to corner at about waist height, above the skirting board (baseboard), and write each length on the sketch straight away.
Measure both diagonals
Corner to opposite corner, both ways. If opposite walls are the same length and the diagonals match, the corners are square; if not, the diagonals let you draw the true shape.
Locate doors and windows
From the nearest corner to the edge of each opening, then its width. For windows, add the sill height and the opening height.
Note heights and fixed items
Ceiling height, beams, radiators, sockets and anything else you cannot move.
Measure the wall thickness
At a door frame, measure from one face of the wall to the other. You need it to place the rooms on either side.
Worked example: a 4.2 × 3.4 m bedroom
The sketch above is a real set of readings. Walls A and C are 4.20 m (13′9″) and walls B and D 3.40 m (11′2″). Both diagonals come out at 5.40 m (17′9″), and a quick check agrees: the square root of 4.2² + 3.4² is 5.40, so the corners are square.
The window in wall A is 1.50 m (4′11″) wide and ends 0.70 m (2′4″) from the corner, with its sill 0.90 m (2′11″) above the floor. The door in wall C starts 0.60 m (2′0″) from its corner and is 0.90 m wide. The ceiling is 2.40 m (7′10″).
The floor inside the walls is 4.20 × 3.40 m = 14.28 m² (about 154 sq ft). If one diagonal had read 5.37 m and the other 5.43 m, the room would be slightly out of square, and you would draw it from the diagonals rather than assume right angles.
From measurements to a plan
You measure a room between its inside faces, but the editor measures walls along their centre lines. So when you type lengths, add one wall thickness to each inside length: a 4.20 m inside wall between two 150 mm walls is 4.35 m centre to centre (13′ 9″ inside becomes about 14′ 3″ with 6 in walls). The example bedroom becomes 4.35 × 3.55 m in the editor, and the room’s area there reads 15.44 m², the area inside the centre lines rather than the floor you would carpet.
Press W, click the first corner and type each length in turn, then double-click to finish. Lock each measured length so tidying up the plan later does not change it.
Common measuring mistakes
A sagging tape
On long walls the tape droops and reads long. Keep it taut and straight, or use a laser.
Measuring over the skirting at one end
Mixing heights gives walls that do not close. Measure every wall at the same height.
Openings from the wrong corner
Note which corner each position is measured from, or a window ends up mirrored on the plan.
Rounding too early
Write what you read, to the centimetre or quarter inch. Round on the plan, not on the sketch.
Forgetting the recesses
Chimney breasts, alcoves and boxed pipes change both the shape and the usable floor.
Measuring checklist
Every wall
Each lettered wall has a length, including short returns.
Both diagonals
Written on the sketch, with a note if they differ.
Every opening
Distance from a named corner, width, and for windows the sill and height.
Heights
Ceiling height and any beam or bulkhead.
Wall thickness
At least one reading at a door frame.
Fixed items
Radiators, sockets, built-in cupboards and the meter or boiler.
What to measure with
Tape measure
A steel tape of 5 m (16 ft) or longer covers most rooms; a second person helps on long walls.
Laser measure
Quick for long walls and ceiling heights, and easy to use on your own.
Squared paper
Keeps the sketch roughly in proportion so the numbers are easy to place.
Room size calculator
Turns a width and length into area and perimeter in both unit systems.
Room dimension calculator
Works the other way: a width and length for a room of the area you want.
Why you might be measuring
New flooring or paint
Measure the clear floor between walls; that is the area you cover.
Buying furniture
Check that a sofa or bed fits with room to walk around it.
Planning a renovation
A measured plan of the home as it is comes before any redesign.
Letting or selling
Room sizes in both units help people judge a home before a viewing.
Frequently asked questions
Should I measure in feet or meters?
Either, but use one system for the whole room. The editor accepts both and converts between them, and the calculators show results in both.
How do I work out a room’s square footage?
Multiply the floor’s length by its width, measured between the inside faces of the walls: 12 ft × 10 ft is 120 sq ft, and 4 m × 3 m is 12 m².
How do I measure an L-shaped room?
Split it into two rectangles, measure each and add the areas. The square footage calculator handles L-shapes directly.
What if the diagonals don’t match?
The room is not quite square. Draw the walls with their measured lengths, then adjust the corners until both diagonals match your measurements; the measure tool (M) checks a diagonal on the plan.
Do I measure from the skirting board or the wall?
Measure the wall above the skirting so every reading is taken the same way. For flooring, the skirting covers the edge, so the wall-to-wall figure is the one to use.