Measure the tread, not the opening
On a closed staircase you measure wall to wall. On an open-sided staircase the tread itself is the reference: measure the full width of the tread including any overhang past the string.
Balancing the reveal
| Tread width | Runner width | Reveal each side |
|---|---|---|
| 36 in | 27 in | 4.5 in |
| 40 in | 30 in | 5 in |
| 42 in | 32 in | 5 in |
| 48 in | 36 in | 6 in |
One open side changes the maths
With a wall on one side and a balustrade on the other, keep the reveal equal on both sides visually — which usually means measuring from the face of the skirting, not the plaster line.
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 calculatorPractical rules for cut-string stairs
- Never let the runner overhang the open edge — it looks unfinished and wears fast.
- Bound or whipped edges matter more here because both edges are permanently on show.
- Check every tread; on older stairs the widths drift by half an inch or more.
- Size to the narrowest tread, then centre the runner on the widest.
- Bullnose or flared bottom steps are measured and fitted separately.
Fixing without a closed string
There is no skirting to hide staples against, so fixings go into the crotch of the step and under the nosing only. Rods can help here — they read as deliberate hardware rather than a compromise.
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 wide should a runner be on open-sided stairs?
Leave 4 to 6 inches of exposed tread on each side, measured from the outer edge of the tread rather than from a wall.
Should a stair runner overhang an open string?
No. Keep the runner inboard of the tread edge so the timber profile stays visible and the edge is not exposed to abrasion.
Do open-sided stairs need bound edges?
Almost always. Both long edges are visible from the hallway, so a whipped or bound finish is the difference between bespoke and homemade.
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.
Size my runner width