The basic formula
Length needed = (number of steps x (tread depth + riser height)) + waste allowance + any extra for a return at top or bottom. Work in one unit system throughout to avoid rounding errors.
13-step worked example
| Measurement | Imperial | Metric |
|---|---|---|
| Tread depth | 10 in | 25 cm |
| Riser height | 7.5 in | 19 cm |
| Per step (tread+riser) | 17.5 in | 44 cm |
| 13 steps raw total | 227.5 in (18.96 ft) | 572 cm (5.72 m) |
| +8% waste/pattern allowance | 245.7 in (20.5 ft) | 618 cm (6.18 m) |
| Rounded order length | 21 ft | 6.2 m |
Know your numbers in 30 seconds
Enter your step count, tread depth and riser height — the stair runner calculator gives you the exact length to order, in metres and feet, with waste included.
Open the stair runner calculatorWhy suppliers add waste margin
- Pattern repeat rarely divides evenly across 13 steps, so full repeats mean offcuts.
- Fitting error: a fitter needs slack to adjust for slightly uneven risers.
- A top or bottom turn onto a landing typically needs an extra 12-18in (30-45cm).
- Natural fibres like sisal and jute can shrink slightly and benefit from extra slack.
Cut-to-length vs pre-made runners
| Type | Flexibility | Typical cost |
|---|---|---|
| Cut from broadloom roll | Any length, any width | $28-$65/linear ft |
| Pre-made fixed-length runner | Fixed lengths only, e.g. 12ft, 15ft, 18ft | $120-$400 total |
Always round up, never down
If your calculated length lands between two roll-cut increments, always round up. Running short mid-installation means a delayed delivery and a visible seam.
Tools and materials, with typical prices
Before starting anything connected to stair runner cut to length: how it works, it helps to know what the job actually costs in tools and consumables, not just carpet. Most of this list is a one-off purchase that will be reused on future stair or rug projects, so it is worth buying reasonable quality rather than the cheapest option.
- Tape measure and chalk line: $15-30 (£12-24), for marking and checking dimensions.
- Utility knife and spare blades: $10-20 (£8-16), for clean cuts through backing.
- Staple gun or tackless strip and knee kicker: $40-150 (£30-120) depending on method.
- Underlay/pad, per step: $3-6 (£2.50-5), skip only where the fibre specifies no pad.
- Seam tape or adhesive for joins: $8-15 (£6-12) per roll or tube.
Safety and building-code notes
Stairs are one of the most common places for a fall in the home, so anything touching stair runner cut to length: how it works should be checked against basic safety practice as well as good looks. Codes vary by jurisdiction but the underlying principles are consistent everywhere carpet meets a staircase.
- Keep nosing build-up modest; a lip much over 3/8 in (10 mm) between the runner and a bare edge becomes a trip hazard.
- Use a slip-resistant backing or pad, particularly on the top and bottom steps where speed is highest.
- Secure every edge fully; a loose corner or lifted seam is the single most common cause of a stair fall on carpeted stairs.
- In rented or multi-occupancy buildings, check local fire and flooring regulations before installing natural fibre runners.
Whatever you decide, get the numbers first: the stair runner calculator doubles as a stair runner length calculator, adding nosing wrap, landings, winders, pattern repeat and waste so you order the right length the first time.
Frequently asked questions
How much extra length should I order for a stair runner?
Add 5-10% on top of the raw tread-plus-riser total, and an extra 12-18in (30-45cm) if the runner turns onto a landing at the top or bottom.
How is stair runner length calculated?
Multiply the number of steps by the sum of one tread depth and one riser height, then add a waste allowance for pattern matching and fitting slack.
Do suppliers cut stair runners to exact length?
Yes, most sell broadloom carpet cut to your specified length by the linear foot or metre, in addition to offering fixed pre-made runner lengths.
How much runner does a 13-step staircase need?
Roughly 19ft (5.7m) raw, or about 21ft (6.2m) once an 8% waste allowance is added, for typical 10in treads and 7.5in risers.
What is the biggest mistake people make with this?
Rushing the measuring or prep stage. Most poor outcomes with stair runner cut to length: how it works trace back to a single measurement taken at the wrong point, or a substrate check skipped to save a few minutes, both far cheaper to fix before the runner is cut than after.
Know your numbers in 30 seconds
Enter your step count, tread depth and riser height — the stair runner calculator gives you the exact length to order, in metres and feet, with waste included.
Calculate the length and cost I needEvery guide is written from hands-on measuring and fitting experience, checked against the calculator’s own maths, and re-reviewed whenever prices or methods change. Read our editorial standards.