The three numbers that make up a runner size
When people ask what size stair runner they need, they usually mean one of three quite different things, and mixing them up is where most ordering mistakes happen. There is width - how wide the strip of carpet is, measured across the stair. There is length - the total run of carpet needed to cover every tread and riser from top to bottom, plus a bit extra at each end for finishing. And there is margin - the strip of bare stair, usually painted or stained wood, left visible on either side of the runner. All three numbers depend on each other, but they are worked out separately and for different reasons, so it helps to treat them as three small calculations rather than one vague guess.
Width is chosen for looks and for the width of the actual staircase; length is dictated by the geometry of the treads and risers, the step count, and whether the flight has a turn or winder; margin is simply whatever is left over once you subtract your chosen runner width from the total stair width, split evenly down each side. None of these numbers are fixed by a building code in most homes - they are aesthetic and practical choices, but they follow well-worn conventions that make a runner look intentional rather than accidental.
Standard widths and what they suit
Runner widths are sold in fairly standard increments, both because looms are set up for particular widths and because certain widths simply look right on certain stairs. In the US, 27 in, 30 in, 32 in and 36 in are the most common stock widths; in the UK, 60 cm, 67 cm, 70 cm, 80 cm and 90 cm are typical. A narrow staircase under 36 in (91 cm) wide overall usually takes a runner of 24-27 in (60-68 cm), leaving a margin of roughly 4-6 in (10-15 cm) each side. A generous 42-48 in (107-122 cm) staircase can comfortably carry a 32-36 in (81-91 cm) runner with a similar proportional margin. As a loose rule, aim for a margin of at least 3 in (7.5 cm) on each side so the runner reads as a deliberate design feature rather than an ill-fitting strip, and no more than about 8-10 in (20-25 cm) so it doesn't look like a runner lost in too much bare tread.
| Overall stair width | Suggested runner width | Typical margin each side |
|---|---|---|
| 32-34 in (81-86 cm) | 22-24 in (56-61 cm) | 4-5 in (10-13 cm) |
| 36-38 in (91-97 cm) | 27-30 in (68-76 cm) | 4.5-5.5 in (11-14 cm) |
| 40-42 in (102-107 cm) | 30-32 in (76-81 cm) | 5-6 in (13-15 cm) |
| 44-48 in (112-122 cm) | 32-36 in (81-91 cm) | 6-8 in (15-20 cm) |
Measure the narrowest point
If the staircase tapers or has a handrail bracket protruding into the tread, measure your overall stair width at the narrowest point on the flight so the runner and its margins clear every obstruction, not just the widest step.
How length is actually built up
Length is where most of the arithmetic lives, because every single step adds its own tread-plus-riser distance, and a flight of 13-16 steps compounds small measuring errors quickly. Each step consumes roughly the tread's walked-on depth plus the riser height plus a small nosing wrap allowance, and you multiply that per-step figure by the total number of steps, then add finishing allowance at the top (where the runner turns onto the landing) and the bottom (where it meets the hall floor or a bar).
How much runner do I need?
Take a common 13-step straight flight with a 10 in (25 cm) tread going and a 7.5 in (19 cm) riser height. Each step needs the tread depth plus riser height plus roughly 1 in (2.5 cm) for the nosing wrap, so about 18.5 in (47 cm) per step. Multiply by 13 steps and you get 240.5 in, or 20 ft (about 6.1 m). Add a combined top-and-bottom finishing allowance of 24 in (60 cm) and you land at roughly 22.5 ft (6.9 m) before waste. Add a 5-10% waste allowance for cutting, pattern matching or an unexpected step variance, and you should order around 23.5-24.5 ft (7.2-7.5 m) of runner. In metric terms, that is a working length of about 6.9 m before waste and 7.2-7.5 m after, which is exactly the sort of tread-by-tread sum a stair runner calculator handles automatically once you enter your own tread count, going and riser height.
Length checklist
- Count every step in the flight, including any winder steps, and measure a sample tread and riser rather than assuming they're identical throughout.
- Multiply the per-step figure by the step count to get the base length.
- Add top and bottom finishing allowances - typically 8-12 in (20-30 cm) combined.
- Add 5-10% for waste, pattern repeat, or fitting error.
- If there's a turn or winder, add an extra allowance for the wider treads at the pivot point.
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 calculatorRunners on turns, winders and landings
A straight flight is the simplest case, but many staircases include a quarter-turn, half-landing, or winder treads that pivot the direction of travel. Winder treads are wider on the outside edge than the inside, so the runner either follows a diagonal cut across each winder or is fitted with a separate custom-cut piece for the turn. Either way, budget significantly more length for a turning flight - often 15-20% over a straight-flight estimate of the same step count - because the outer edge of each winder eats more material than a straight tread would. If your stairs have any turn at all, it is worth having a fitter measure in person rather than relying purely on a desk calculation, since winder geometry varies house to house.
Margins and how they affect perceived size
The margin either side of the runner does more visual work than people expect. A wide margin on a narrow stair can make the runner look undersized and lost, while a tight margin on a wide stair can make the whole staircase feel cramped, since the eye reads the exposed wood as part of the overall proportion. If you're unsure, lay masking tape at your proposed runner edges before ordering and live with it for a day or two; small proportion shifts are much easier to spot in person than on a spec sheet.
Width and length interact with pattern repeat
If you've chosen a patterned runner - stripes, a border, a geometric repeat - your final width and length numbers may need to be nudged so the pattern lands cleanly rather than cutting off mid-motif at a nosing. This is a secondary check to run once you have your base width and length figures, not something to worry about before you've settled the fundamentals above.
Getting the numbers right before you order
Because a stair runner is a made-to-length product, not something you can simply return and reorder for free, it pays to double-check your figures before placing an order. Re-measure a second tread and riser partway down the flight to confirm consistency, confirm your chosen width against the narrowest point of the stair, and run the whole calculation through a stair runner length calculator so you have a second, independent check on your arithmetic before it goes to a supplier or fitter.
Still deciding on material, width or pattern? Our hub on stair runners compares weaves, widths, backings and fitting styles side by side, then hands the numbers straight to the calculator.
Frequently asked questions
What is a standard stair runner width?
Common widths are 27, 30, 32 and 36 in (68, 76, 81 and 91 cm) in the US, or 60, 67, 70 and 80 cm in the UK. The right width depends on your overall stair width - aim for a margin of roughly 3-8 in (7.5-20 cm) of bare stair showing on each side.
How is stair runner length calculated?
Multiply each step's tread depth plus riser height plus a small nosing allowance by the total number of steps, then add finishing allowance at the top and bottom of the flight, plus 5-10% waste. A stair runner calculator does this arithmetic automatically once you enter your tread count and dimensions.
How much margin should be left either side of a runner?
Most fitted runners leave 3-8 in (7.5-20 cm) of bare stair visible on each side, scaled to the overall stair width. Too little margin looks cramped; too much makes the runner look undersized, so match the margin proportionally to how wide the staircase actually is.
Do winders and turns need extra runner length?
Yes. Because winder treads are wider on their outer edge, a turning flight typically needs 15-20% more runner length than a straight flight with the same number of steps. Getting a fitter to measure winders in person is safer than a desk estimate.
Can I use the same width runner on every stair in the house?
Only if every flight has a similar overall stair width. Landing runs, secondary staircases and attic stairs often have different widths, so measure each flight separately rather than assuming one width fits the whole house.
Does a patterned runner change the sizing?
It can. Once you've settled your base width and length, a patterned or striped runner may need the length rounded up to the nearest full repeat so the motif doesn't cut off awkwardly at a nosing, adding a modest amount of extra material.
What happens if I measure the tread depth wrong?
A small error compounds across every step - being off by even half an inch on a 13-step flight adds up to over six inches of miscalculated length. Always measure a couple of treads and risers rather than a single one, and cross-check with a calculator before ordering.
Is there a minimum runner width for safety?
There's no universal legal minimum for a residential runner, but a strip narrower than about 22 in (56 cm) rarely covers the full walked-on path of a foot placed centrally on the tread, reducing the practical grip and cushioning benefit the runner is meant to provide.
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.
Work out your exact stair runner sizeEvery 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.