How to measure a room that isn't square
Almost no room is a true rectangle. Here is how to measure one so the last row fits, using a tape, a pencil and two diagonals.
Walls drift. A room that looks rectangular is often a few millimetres out over its length, and sometimes a lot more. On a 4 m run you won’t see it, but the floor will: the last row tapers, a gap opens along the skirting, or a board that fitted at one end is 15 mm short at the other.
Measuring properly takes ten minutes and saves a pack. This is the method we built Layo around.
1. Sketch the room and name the corners
Draw the room roughly on paper, walking round it clockwise. Give every corner a letter: A, B, C and so on. Include every step, nib and chimney breast. If a corner exists in the real room, it gets a letter on the sketch.
2. Measure every wall, corner to corner
Measure each wall at floor level, where the boards will actually go, not at waist height. Write the figure along the wall on your sketch. Read the tape to the millimetre and don’t round.
If a wall has a doorway, measure to each side of the opening too. You will need those numbers when the boards run through into the next room.
3. Take the diagonals
Four wall lengths don’t fix the shape of a room. The same four numbers fit a perfect rectangle and a slightly squashed one. The diagonals are what pin it down.
- In a four-cornered room, measure both diagonals: A to C and B to D.
- If the two diagonals of a rectangle differ, the room is out of square, and the difference tells you by how much.
- For an L-shaped or more complicated room, split it into triangles in your head and measure one diagonal for each.
If you only remember one thing: wall lengths tell you the size, diagonals tell you the shape.
4. Check the numbers agree
Before you leave the room, check that the measurements are consistent. With a triangle, any two sides must add up to more than the third. With a quadrilateral, the diagonals should match what the walls allow. If a figure looks off, measure it again now. It is much cheaper than finding out halfway across the floor.
This is the check Layo runs for you. Enter the walls and diagonals, and it works out the true shape, tells you if a measurement doesn’t add up, and says which diagonal is still missing.
5. Note what the boards need
While you are there, write down the details that change the layout:
- Where the light comes from. Boards usually run toward the main window.
- Door thresholds. Where the floor stops and what it meets.
- The expansion gap the maker asks for at every wall, usually printed on the pack.
- Heating pipes, floor outlets and anything fixed to the floor.
With that, you can plan the whole floor before you open a box, and know the width of the last row before you cut the first one.