What 'run' means on a staircase
Total run is the horizontal distance from the face of the first riser to the face of the last riser, measured along the floor, not along the slope of the stringer. It is distinct from 'going', which is the horizontal depth of a single tread — run is simply going multiplied by the number of treads (with a small adjustment if the top step doubles as the landing floor). A 13-tread flight with a 250mm going has a total run of 3.25m (10ft 8in), which is the length of floor, hallway or opening the staircase needs before you add any landing.
It is easy to confuse run with the overall footprint of a staircase, but the two are not the same. The footprint also includes the width of the flight and any landing, winder or turn, so a staircase with a generous run in a straight line can still have a smaller footprint than a shorter, tighter staircase that turns through 90 or 180 degrees and needs a landing platform.
| Number of treads | Going | Total run |
|---|---|---|
| 12 | 220mm (8.75in) | 2.64m (8ft 8in) |
| 13 | 250mm (9.8in) | 3.25m (10ft 8in) |
| 14 | 265mm (10.4in) | 3.71m (12ft 2in) |
| 15 | 280mm (11in) | 4.20m (13ft 9in) |
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 calculatorCalculating run from rise, angle or code minimums
There are three practical ways to arrive at a run figure, depending on what you already know. If you know riser height and the number of risers, calculate the going first (using the riser calculator or a comfort formula), then multiply by the number of treads. If you know your target pitch angle, run = rise / tan(angle) gives the total run directly. If you are working from a fixed floor opening, you can work backwards: divide the available run by your intended riser count to check what going that leaves you with, and confirm it clears the 220mm (UK) or 10in (US) minimum.
- Decide the total rise (floor to floor height) first, since this rarely has flexibility.
- Choose a target riser height within 170-200mm (6.7-7.9in) and calculate the number of risers needed.
- Look up or calculate a comfortable going for that riser height using the 2R+G formula.
- Multiply going by the number of treads to get the total run.
- Compare that run against the available floor space — if it does not fit, either steepen the pitch within legal limits or consider a winder/turn to reduce the footprint.
Headroom and how it constrains run
Headroom — the clear vertical space above the pitch line of the stairs — is the constraint that most often forces a compromise on run. UK Approved Document K requires a minimum headroom of 2.0m (2.0m for a private stair, sometimes reduced to 1.9m at the stair's centre line in tight loft conversions under specific conditions), while the US IRC requires a minimum of 6ft 8in (2.03m) measured vertically from the nosing line. A shorter run with a steeper angle can sometimes solve a headroom problem, but only within the maximum angle limits already covered by the stair angle calculator.
| Region | Minimum headroom | Measured from |
|---|---|---|
| UK (Approved Document K) | 2.0m (reduced allowance in some loft cases) | Pitch line, vertically |
| US (IRC R311.7.2) | 6ft 8in (2.03m) | Nosing line, vertically |
Run and headroom fight each other
Increasing run by lowering the angle usually helps headroom at the top of the flight but can worsen it partway down if there is a ceiling change, beam or floor opening above. Always check headroom at every point along the flight, not just at the top and bottom.
Run, landings and turns
A landing effectively resets the run calculation: each flight either side of a landing is calculated independently, and the landing itself needs its own floor space, typically at least as deep as the staircase is wide, with UK guidance requiring a landing at least as long as the stair width and US IRC requiring a minimum landing dimension equal to the width of the stair, up to 48in (1.22m), in the direction of travel. Adding a 90-degree turn with a landing generally uses less linear floor space than a single long straight run, which is why turned staircases are common in smaller homes even though they are more complex to build.
Floor space planning beyond the flight
Beyond the strict run measurement, allow clear floor space at the top and bottom of the flight for safe use: UK guidance expects at least 400mm of clear space beyond the bottom step before a door or obstruction, and US practice generally follows similar clearances at both landings. If your total run calculation leaves the bottom step opening directly into a doorway swing or a narrow hallway, the numbers may technically comply with stair regulations while still creating a genuinely awkward, unsafe pinch point.
- Add clear floor space at both ends of the run, not just enough for the treads themselves.
- Check door swings near the top and bottom of the flight against the finished run.
- Remember that a runner's tucking allowance at top and bottom does not affect run — it only affects material length.
- If the flight turns, calculate each straight section's run separately and add the landing depth between them.
Cost implications of changing the run
Extending the run of an existing staircase to make it shallower usually means enlarging the floor opening upstairs, which is a structural alteration typically costing £2,000-£5,500 in the UK or $3,000-$7,000 in the US once joist work and building control sign-off are included. Shortening the run by steepening the pitch within legal limits, by contrast, can sometimes be done by rebuilding just the stringers and treads for a fraction of that cost, since it avoids touching the floor structure — worth discussing with a structural engineer or joiner before assuming a full opening enlargement is necessary.
Once the geometry is settled, the finishes follow: work out the covering with the stair runner calculator on the homepage, and use the same stair runner length calculator to price the carpet or runner before you order it.
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 calculatorWhatever 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
What is the run of a staircase?
The run is the total horizontal distance a staircase covers, measured from the face of the bottom riser to the face of the top riser. It equals the going of one tread multiplied by the number of treads in the flight, and it is separate from the sloped length of the stringer.
How do I calculate the total run of a staircase?
Multiply your chosen tread going by the number of treads in the flight. For example, 13 treads at a 250mm (9.8in) going gives a total run of 3.25m (10ft 8in), before adding any landing space at the top or bottom.
How much floor space does a staircase need?
Beyond the calculated run, allow clear space at both ends — UK guidance suggests at least 400mm clear beyond the bottom step — plus the width of the flight and any landing depth if the stair turns. A straight 13-step domestic flight typically needs 3.5-4m (11.5-13ft) of usable length including clearances.
What is the minimum headroom required over a staircase?
UK Approved Document K requires a minimum of 2.0m headroom over most of a private stair, with limited reduced allowances in loft conversions. The US IRC requires at least 6ft 8in (2.03m), measured vertically from the nosing line at every point along the flight.
Does adding a landing reduce the run I need?
A landing splits a staircase into shorter flights, each with its own run, which can reduce the overall linear floor space needed compared with one long straight flight, though the landing itself needs its own footprint, typically at least as deep as the stair is wide.
Does total run affect how much stair runner carpet I need?
Not directly — runner length is driven by the going and riser height per step rather than total run on its own. However, since run and going are directly related, checking your run calculation alongside the stair runner calculator will catch any inconsistency before you order material.
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 my stair runEvery 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.