Home Improvement
Carpet Calculator
Measure the room, add waste, and convert to square metres (or feet) and approximate roll length.
How much carpet do I need?
Carpet is sold by the roll width and cut length, not only by neat room area. Enter room dimensions and the roll width you will buy, then allow waste for matching patterns, doorways and the odd mis-cut. Underlay, gripper rods and threshold bars are separate purchases — this tool focuses on carpet area and approximate linear metres from a given width. Irregular rooms need segmented rectangles added together; L-shapes that you flatten into one big rectangle usually over-order. Pattern repeats on bold designs can push waste well past the textbook 10%. Related flooring maths: flooring calculator for planks and laminate, and tile calculator when you are comparing hard finishes. Stairs deserve their own take-off; do not squeeze them into a single rectangle. Estimate only — not a fitter’s survey or Building Regulations advice. Ask the retailer whether prices are per m² or per running metre of roll, then reconcile with this area figure before you pay a deposit. Keep leftover offcuts labelled by batch for future repairs when the range is discontinued.
Worked example
A room 4.5 m × 3.2 m is 14.4 m². With 10% waste you need about 15.8 m². On a 4 m wide roll, length ≈ 15.8 ÷ 4 = 3.95 m — typically ordered as 4.0 m of roll (16 m²). A patterned carpet at 15% waste needs about 16.6 m², so closer to 4.2 m of the same roll.
Limits and assumptions
Assumes a rectangular room and a single roll width. Stairs, bay windows and seams need a fitter’s plan. Does not check underfloor heating compatibility or moisture.
Frequently asked questions
How much waste should I allow?
Around 10% for plain carpet in a simple room; more for patterns, diagonals or many doorways.
What is roll width?
Common UK widths include 4 m and 5 m. Your supplier’s width drives the cut length you order.
Should I include underlay in this total?
No — calculate underlay area separately, usually matching the carpet area with its own trim allowance.
How do stairs work?
Measure treads and risers separately or ask the fitter; stair waste factors differ from flat rooms.
Metres or feet?
Stay consistent. UK retailers quote m², so metres are usually easiest.