How to Measure a Room for Carpet

Tools You’ll Need

• ✓A tape measure — a proper retractable steel tape rather than a fabric dressmaking one, ideally 5m or longer.
• ✓Paper and pen, or a notes app, to sketch the room shape as you go.
• ✓A calculator, or our room size measurer tool to do the maths for you.
• ✓A second pair of hands for anything larger than a small room — a tape measure sags and drifts off-square over long distances on your own.

Measuring a Rectangular Room

Measure the length and width at floor level, at the widest point of the room in each direction — not at skirting-board height, where trim and architraves can shave a centimetre or two off the true reading. Multiply length by width for the floor area in square metres, then add a waste margin on top before you buy anything.

Why the waste margin matters

Carpet doesn’t come in whatever width your room happens to be — it’s sold off a fixed-width roll, and offcuts, trimming around doorframes, and awkward corners all use up more than the bare floor area suggests. A 10% margin on top of the raw area is a sensible planning figure for a standard rectangular room.

Measuring an L-Shaped Room

Split the room into two rectangles on your sketch — a main rectangle and the smaller “leg” of the L. It doesn’t matter exactly where you draw the dividing line, as long as the two rectangles together cover the whole floor without overlapping. Measure and calculate each rectangle’s area separately, then add the two totals together before applying the waste margin to the combined figure.

Bay windows, chimney breasts and other alcoves work the same way — treat each as its own small rectangle (or triangle, measured as half a rectangle) and add it to the running total rather than trying to eyeball an irregular shape as one figure.

Measuring Stairs

Stairs are the trickiest thing to measure accurately yourself, which is exactly why most fitters use a standard per-step allowance rather than measuring every individual tread and riser. A widely used allowance is around 0.55m per step, covering the tread, the riser and a little wrap-under — multiply that by the number of steps for a workable planning figure.

Winders, bullnose steps and unusually deep or shallow treads all need adjusting from the standard figure, and it’s genuinely easy to get wrong from a tape measure alone — see our stair carpet fitting page, and consider a free professional measure for anything beyond a simple straight staircase.

Roll Widths & Waste

UK broadloom carpet is sold in fixed roll widths, usually 4m or 5m, and you always pay for the full width of whatever length you cut — even if your room is narrower than the roll. A room that fits neatly within one roll width in either direction wastes far less than one that needs a wider roll or extra strips joined with a seam.

Which way the roll is laid — along the room’s length or rotated 90° along its width — changes how much you actually need to buy, and it’s rarely the orientation people guess first. Our roll width & waste estimator compares both orientations for your exact room and tells you which wastes less, and whether you’ll need a seam at all.

Common Measuring Mistakes

• ✓Measuring at skirting height instead of floor level, which under-reads the true width.
• ✓Forgetting alcoves, bay windows or chimney breasts, which under-states the total area.
• ✓Ignoring pattern repeats on patterned carpet, which can need extra length to line up across a seam.
• ✓Skipping the waste margin entirely and ordering the bare floor area, leaving no room for offcuts or trimming.

When to Leave It to the Fitter

Your own measurements are a strong planning figure for budgeting and shopping, but they shouldn’t be the final word on what gets cut and ordered. For anything beyond a simple rectangular room — an L-shape, a staircase, a room with several alcoves, or any job where seam placement matters — a professional measure removes the guesswork entirely.

We offer a free measure alongside every carpet fitting quote, using proper tools and trade experience to confirm exact quantities and the best layout before anything’s cut. Message us your postcode and rough dimensions and we’ll arrange it.