How much carpet do your stairs need? Enter the steps, tread and riser to get the length to cut off a 4 m or 5 m roll, how the strips fit across it, the landing, gripper and underlay, with the working shown.
Measure the stairs themselves, starting at the top. Guides such as Tapi's measure from the top down because that's the way the pile runs.
Carpet per step is the tread plus the riser plus the allowance: 250 mm + 200 mm + 50 mm = 500 mm.
Stair carpet runs with its length, the way it comes off the roll, up and down the stairs, as the Carpet and Rug Institute's installation standard, CRI 105, recommends. So each strip is the stair width plus trimming, and the strips sit side by side across the roll.
The calculator fits as many strips across the roll as it can, shares the steps between them evenly and cuts the roll at the longest strip. A landing goes wherever it adds least: beside the strips, under the shorter ones or after them. You pay for the full roll width, so the offcut is part of the price.
0.90 m wide stairs, 250 mm tread, 200 mm riser, 50 mm allowance a step, 50 mm trimming each side.
| Stairs | Roll | Strips (steps) | Cut | Carpet bought | Offcut | Gripper |
|---|---|---|---|---|---|---|
| 13 steps, straight | 4 m | 4, 3, 3, 3 | 2.00 m | 8.00 m² | 1.50 m² | 26 lengths |
| 13 steps, straight | 5 m | 3, 3, 3, 2, 2 | 1.50 m | 7.50 m² | 1.00 m² | 26 lengths |
| 13 steps + 1.20 × 1.00 m landing | 4 m | 4, 3, 3, 3 + landing | 2.80 m | 11.20 m² | 3.27 m² | 26 lengths + landing |
| 14 steps, 1.80 × 0.90 m landing after step 7 | 4 m | 4, 3 + 4, 3 + landing | 3.40 m | 13.60 m² | 4.70 m² | 28 lengths + landing |
| 14 steps, 1.80 × 0.90 m landing after step 7 | 5 m | 4, 3 + 4, 3 + landing | 2.00 m | 10.00 m² | 1.10 m² | 28 lengths + landing |
| 13-step runner, 0.60 m wide | Runner | One length | 6.50 m | 3.90 m² | None | 13 lengths |
A 5 m roll takes an extra strip across and shortens both cuts here. Try both widths, as long as the carpet comes in both.
CRI 105 notes that most manufacturers recommend the pile runs down the stairs, and Online Carpets says it should run across the landing and down the stairs the same way. Cutting every piece along the roll keeps them all the same way round. The carpet's own fitting instructions come first.
CRI 105 puts gripper on every tread with the pins towards the riser and, for a waterfall finish, on the risers too with the pins pointing down. Carpet Underlay Shop's guide fixes it at the back of each tread and the base of each riser. The calculator counts both strips per step at the stair width, in the 1.52 m lengths Interfloor sells its stair gripper in: on 0.9 m stairs each length cuts one strip, so 13 steps need 26. A landing needs gripper along its edges too.
For underlay, Carpet Underlay Shop cuts a piece for each tread to sit inside the gripper, and CRI 105 says separate underlay should go over the stair nose.
A landing wider than the roll needs a join, and Brintons' installation guide says to keep seams and cross joins away from stair noses.
Strips cut side by side all start at the same point in a pattern, but on the stairs each one has to carry on from the step above, so the calculator adds one pattern repeat per row of pieces for lining up. Check the carpet's fitting instructions.
A runner comes at its finished width, so you need one length over every step, plus any landing it crosses. If it turns a corner, measure each straight run.
Loose or worn carpet on stairs is a trip hazard. RoSPA's advice is that stairs should be carefully maintained, and damaged or worn carpet repaired or removed. Stair carpet has to be fitted tight so it can't move or lift, so if in doubt, use a professional fitter.
This calculator sizes one staircase at a time. BillyBot's cutting plans handle stairs as part of the whole job, and BillyBot, the AI operator for flooring businesses, runs the office side of the business from first enquiry to final invoice. See BillyBot's cutting plan software and flooring quoting, or size the rooms with the carpet calculator.
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It depends on the steps and the roll. For 13 steps 0.9 m wide at 500 mm a step (a 250 mm tread, 200 mm riser and 50 mm allowance), with 5 cm trimming each side, four strips fit across a 4 m roll, so you'd buy a 2 m cut: 8 m² of carpet.
Start at the top. Count the steps, then measure the width at the widest point, the tread from the back to the front of the nosing and the riser from one tread to the next, and add an allowance for the nosing and trimming. Measure landings and each winder separately.
Down the stairs. The Carpet and Rug Institute's installation standard notes that most manufacturers recommend it, which is why UK retailers' guides measure stairs from the top down. Check the fitting instructions for your carpet.
Allow a strip at the back of each tread and one at the foot of each riser, each about the stair width. 13 steps 0.9 m wide need 26 strips, or 23.4 m. Interfloor's stair gripper comes in 1.52 m lengths, and each cuts one 0.9 m strip, so you'd need 26 lengths.
A runner comes at its finished width, so you need one length: the tread, riser and allowance for one step, times the number of steps, plus any landing it crosses. 13 steps at 500 mm is 6.5 m.
No. Winders are tapered treads, each a different shape, so measure each one at its widest points. The calculator covers straight flights and landings, and BillyBot's cutting plans handle stairs, winders included, as part of the whole job.
You buy the full roll width over the length you cut, even where the stairs only use part of it. Fitting as many strips across as possible and tucking a landing under the shorter strips keeps it down, and it's worth trying both roll widths.
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