Measuring Open-Sided Stairs for a Runner

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

Practical 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.

Measuring method, step by step

1. Measure the full width of the widest tread, including any overhang past the string or balustrade posts.
2. Measure the narrowest tread on the same flight — older or hand-built stairs often vary by half an inch or more.
3. Choose your runner width based on the narrowest tread, so the reveal never disappears on any step.
4. Mark a centre line up the flight using a chalk line or laser, referencing the tread edges rather than the wall.
5. Dry-lay a length of scrap material or masking tape at the chosen width on two or three steps to check the reveal looks right before committing to an order.

Two open sides vs one open side

Cost implications of open-sided stairs

Expect to pay 15-25% more in fitting labour on open-sided or cut-string stairs compared with a closed staircase of the same length. The extra cost comes from templating each tread individually, binding both edges of the runner, and the slower, more careful fixing method required when there is no skirting to hide behind.

• Binding or whipping both long edges: $3–$8 per linear foot on top of the base runner cost.
• Rod brackets fitted into the open tread edge: $15–$40 per rod depending on bracket style.
• Templating irregular treads: often billed as an extra hour or two of labour at the fitter's standard rate.

Common mistakes on open-sided flights

• Measuring from the wall on the closed side only and assuming the open side matches — it rarely does exactly.
• Choosing a runner width based on the average tread rather than the narrowest one.
• Letting the runner run right to the tread edge, which looks fine on day one but frays fast under foot traffic and shoe scuffs.
• Skipping bound edges to save money, then finding the raw edge unravels within a season of use.

Handling a curved or bullnose bottom step on an open flight

Open-sided staircases very often finish in a curved bullnose or a flared bottom step, since the open side gives the joiner room for a decorative sweep. This step cannot be measured with a straight tape and needs a template — either a card pattern cut to the exact curve, or a flexible measuring tool pressed against the nosing to capture the profile. Bring this template to the supplier or fitter rather than trying to describe the curve in numbers; a half-inch error on a bullnose is far more visible than the same error on a straight tread.

Balustrade posts and newels

• Where a newel post interrupts the run, the runner is usually cut and finished at that step rather than notched around the post.
• Measure the clear tread width on both sides of any intermediate newel separately, since it is often narrower than the rest of the flight.
• A fitter will typically neaten the cut edge against a post with a small return of binding rather than trying to hide it under trim.
• If posts are being replaced or the balustrade renovated at the same time, always fit the runner after the joinery work is finished, not before.

Rod placement on open-sided stairs

Because both edges of the runner are visible on an open-sided flight, stair rods do more visual work here than on a closed staircase. Brackets are typically fixed into the underside of the tread nosing rather than the stringer, and the rod itself should sit proud of the runner by a small, consistent amount at every step — usually around half an inch either side. On stairs with only one open side, some homeowners choose a rod that appears to run the full width but is only genuinely functional, fixed with brackets, on the open side, with the wall-side end sitting in a simple socket.

Comparing open-sided fitting methods

Tools for measuring an open-sided flight

• A steel tape rather than a fabric one, since fabric tapes sag and distort measurements taken across an open tread.
• A laser level or chalk line to establish a true centre line up the flight, since the open edge is rarely a reliable straight reference.
• A flexible curve template for any bullnose or flared bottom step.
• A notebook or phone template to record each tread's width individually rather than relying on memory once you reach the supplier.

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.

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.