How to Measure a Room
Floor area, perimeter, wall area and what to do with an L-shape.
Measure at floor level, twice
Run the tape along the skirting rather than at waist height. Measure each wall at two points — rooms are rarely perfectly square, and the larger figure is the safe one to work from.
L-shaped rooms: split into rectangles
Draw the plan, split it into two rectangles, calculate each area and add them. For perimeter, walk the outside edges only — do not count the imaginary dividing line.
Record ceiling height separately
Wall area equals perimeter × ceiling height. Note any sloped ceilings and treat those walls as triangles: half the base times the height.