Flooring
Carpet Calculator
Estimates carpet area with seam allowance and roll widths
Updated 5 June 2026 · Live
What this tool does
Estimates carpet area with seam allowance and roll widths.
Formula Used
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How the carpet calculator works
Estimates the carpet area to order for a room, allowing for roll width and seams. The calculator lays full-width drops along the longer dimension to avoid unnecessary seams, adds your wastage margin, and returns the area to order with an indicative cost. Every figure is an estimate — site conditions always move the final number.
Typical UK carpet wastage
Common UK trade allowances are around 10% for a straightforward rectangular room, rising to about 15% for awkward shapes, stairs, or a bay. A large pattern repeat that has to be matched across drops needs more again. Our defaults reflect common UK trade allowances, and can be adjusted upwards for non-standard rooms or downwards where experience supports a lower figure.
What this tool does not do
It does not replace a professional quote, factor regional pricing, assess structural adequacy, or confirm Building Regulations compliance. Those remain the responsibility of a suitably qualified designer, surveyor, or your building control officer.
On-site considerations for carpet
Carpet is only as good as what it sits on. The subfloor should be clean, dry, and level, with a suitable underlay chosen for the room and any underfloor heating. Gripper rods around the perimeter and a tidy threshold or door bar at each doorway keep the carpet tensioned and the edges secure.
Building Regulations and compliance
Ground-floor finishes in new work must sit over a DPM and achieve the Approved Document C moisture targets. Electric underfloor heating is covered by Part P. When in doubt, a pre-application enquiry to the local authority can give early clarity, which is usually simpler than retrospective correction.
Before you order
Order all the carpet for one room from a single roll and batch, because pile direction and dye lot can shade differently between rolls. Keep the larger offcuts for future repairs, stair patches, or door bars. Cross-checking the calculator's output against a supplier quote helps catch differences in pricing assumptions — confirm the roll width, pile direction, and delivery timescale against your programme.
Adjusting the defaults
Every input in this calculator is editable. Enter your own room dimensions, roll width, wastage allowance, and price — the output recalculates instantly. If the defaults feel off for your room or product, your own numbers always override them.
Using this carpet calculator alongside other BuildMetricLab tools
This calculator works best as part of a planning workflow. Pair this estimate with our vinyl, tile, and hardwood flooring calculators to compare options across a project before you pick up the phone to a supplier. All BuildMetricLab tools run entirely in your browser — no sign-up, no data sent anywhere, and every formula is shown on-page so you can audit the maths.
Sources & methodology
Estimates the carpet area to order by laying full-width drops along the room's longer dimension to minimise seams, then adding a wastage allowance: A = ⌈min(L,W)/rW⌉ · rW · max(L,W) · (1+w). Every result is calculated from the values you enter, and all inputs are editable.
Frequently asked questions
Are carpet calculator results accurate enough to order materials?
Use them as a starting estimate only. Verifying the final quantity with your supplier or contractor before ordering is good practice — site conditions, wastage and cut-offs all affect the true figure.
What wastage percentage should I use?
The calculator defaults to the typical UK trade allowance for carpet. A higher allowance suits awkward shapes, stairs, or a large pattern repeat that must be matched across drops; a lower one can work for a simple rectangular room. Values below the default may underestimate offcuts.
Does this replace professional advice?
No. This tool is a planning estimator. For works that affect structure, Building Regulations, Party Wall, gas, electrics, drainage to a sewer, or similar, consult a suitably qualified professional.
Can I change the unit prices?
Yes — every price field is editable. Plug in your supplier's quote to get a total that matches your project.
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