Three meanings of "stair length"
| Meaning | What it measures | Used for |
|---|---|---|
| Total run | Horizontal footprint, floor to floor | Checking the stair fits the available space |
| Stringer (pitch) length | Diagonal board length along the slope | Ordering stringer stock and cutting the board |
| Runner/carpet length | Fabric distance over every tread and riser surface | Ordering carpet or runner material |
Total run
Total run = number of treads × tread depth. For 13 risers (12 treads) at 10in: 12 × 10 = 120in, or 10ft. This is the number to check against your available floor space before committing to a straight flight — if the stairwell opening is shorter than this, you need a turn, a shorter tread run (within code limits), or fewer/steeper steps.
Stringer (pitch) length
The stringer follows the diagonal hypotenuse of the total rise and total run, not the horizontal run alone. Using the Pythagorean theorem: stringer length = √(total rise² + total run²). For 97.5in total rise (13 × 7.5in) and 120in total run: √(97.5² + 120²) = √(9506.25 + 14400) = √23906.25 = about 154.6in. Add a margin at the top and bottom for the horizontal cuts (typically 6-12in extra stock) when ordering board length.
| Step | Value |
|---|---|
| Total rise (13 × 7.5in) | 97.5in |
| Total run (12 × 10in) | 120in |
| Pitch length (Pythagorean) | √(97.5² + 120²) = 154.6in |
| Stock to order (+ margin) | About 162-168in per stringer |
Runner/carpet length
Runner length follows the tread-plus-riser path up every step: length = steps × (tread depth + riser height), plus nosing wrap if wanted, plus a waste allowance. For 13 steps at 10in tread and 7.5in riser: 13 × (10 + 7.5) = 13 × 17.5 = 227.5in. Add a typical 10% waste margin: 227.5 × 1.10 = 250.25in, or about 6.36m / 20ft 10in.
Runner length uses all 13 steps, stringer/run use 12 treads
This is the detail that trips people up: total run and stringer length are based on tread count (12, since the top riser meets the upper floor), but runner length covers every riser including the last one, which is why it uses the full 13-step count.
Comparing the three for the same flight
| Measurement | Formula | Result for 13 steps, 7.5in riser, 10in tread |
|---|---|---|
| Total run | 12 treads × 10in | 120in (10ft) |
| Stringer length | √(97.5² + 120²) | ≈154.6in, order ≈162-168in stock |
| Runner length | 13 × (10+7.5) × 1.10 waste | ≈250.25in (≈6.36m) |
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 calculatorMetric version
For a 2700mm rise, 170mm riser, 280mm tread flight (16 risers, 15 treads): total run = 15 × 280 = 4200mm. Stringer length = √(2700² + 4200²) = √(7,290,000 + 17,640,000) = √24,930,000 ≈ 4993mm. Runner length = 16 × (280+170) × 1.10 = 16 × 450 × 1.10 = 7920mm ≈ 7.92m.
Which calculator to use for which question
- Checking if the stair fits the available floor space: total run, via the stair calculator.
- Ordering stringer board stock: pitch length, via the stair stringer calculator.
- Ordering carpet or a runner: runner length, via the stair runner calculator.
- All three: they share the same underlying rise/run numbers, so calculate riser and tread once and feed the same figures into each.
Whichever length you're solving for, always add a margin: 6-12in of extra stringer stock for the horizontal end cuts, and 10-15% waste on runner or carpet length to allow for pattern matching, trimming and mistakes on site.
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
What does 'stair length' mean?
It depends on context — total run (horizontal footprint), stringer/pitch length (diagonal board length for cutting), and runner/carpet length (fabric distance over every tread and riser) are all commonly called stair length but produce different numbers.
How do I calculate total run?
Multiply the number of treads (one fewer than the number of risers) by the tread depth. For 13 risers at 10in tread depth, that's 12 × 10in = 120in.
How do I calculate stringer length?
Use the Pythagorean theorem on the total rise and total run: stringer length = √(total rise² + total run²), then add 6-12in of stock for the horizontal end cuts.
How do I calculate carpet or runner length?
Multiply the number of steps by (tread depth + riser height), then add a waste allowance of roughly 10-15% for trimming and pattern matching.
Why does runner length use a different step count than total run?
Runner length covers every riser including the last one where it meets the upper floor, while total run and stringer length are based on tread count, which is one fewer than the riser count.
Is stringer length the same for every stringer in a flight?
Yes for a straight, level flight — every stringer follows the same pitch line, so they're cut to the same length, just spaced across the stair's width.
How much extra stringer stock should I buy?
Typically 6-12in beyond the calculated pitch length, to allow for the horizontal cuts at the top and bottom of the stringer.
Does a landing or turn change these calculations?
Yes — each flight either side of a landing is calculated separately, and the landing's own flat length is added on top for total run and runner length calculations.
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 rise and run calculatorEvery 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.