Treads vs. risers: the count is always different
A flight with 13 risers has 12 treads, not 13, because the top of the flight lands on the floor above and does not need a tread of its own. This one-off difference trips up a surprising number of material orders, so always calculate risers first from total rise, then subtract one for the tread count.
Working out the numbers
- Measure total rise: the vertical distance from finished lower floor to finished upper floor.
- Choose a target riser height, commonly in the region of 175-200mm (7-8in) for residential stairs, subject to your local code maximum.
- Divide total rise by the target riser height and round to a whole number of risers.
- Recalculate the exact riser height by dividing total rise by that whole number, so every riser is identical.
- Subtract one from the riser count to get the tread count.
- Multiply tread count by tread width to estimate board footage, adding waste allowance for cutting.
| Total rise | Target riser height | Risers (rounded) | Exact riser height | Treads |
|---|---|---|---|---|
| 2,600mm / 102.4in | 180mm / 7.1in | 14 | ≈185.7mm / 7.31in | 13 |
| 2,850mm / 112.2in | 175mm / 6.9in | 16 | ≈178.1mm / 7.01in | 15 |
| 3,000mm / 118.1in | 190mm / 7.5in | 16 | ≈187.5mm / 7.38in | 15 |
Every riser in a flight should be within a very small tolerance of every other riser — commonly a few millimetres at most under most codes — because an uneven step is a well-documented trip hazard. This is exactly why the calculation recalculates an exact riser height rather than simply using your rounded target figure.
Material take-off for treads
| Component | Typical thickness | Sizing note |
|---|---|---|
| Tread board | ≈32-44mm / 1.25-1.75in | Width = going + nosing overhang, commonly 20-30mm / 0.75-1.25in |
| Riser board | ≈18-25mm / 0.75-1in | Height = exact riser height minus tread thickness allowance |
| Stringer (per side) | ≈32-44mm / 1.25-1.75in | Length ≈ pitch-line length of the flight plus horizontal allowance at each end |
Order tread and riser stock with a waste allowance, commonly around 10-15% for solid timber to allow for defects, knots and cutting losses, and a little less for engineered or MDF risers which are more consistent. Always dry-fit or template the first tread and riser before batch-cutting the rest of the flight.
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 calculatorOpen riser and closed riser take-offs differ
An open-riser stair needs no riser boards at all, which changes the material list substantially — you are ordering treads and stringers only, though open treads are often thicker to remain rigid without a riser behind them for support. Confirm your riser style before pricing material, since it changes both the board count and the minimum tread thickness needed.
Winders and landings in the take-off
Winder treads are wider at one end than the other and are usually templated individually rather than cut to a single repeated size, so budget extra material and extra cutting time for any winder section. A landing is not a tread in the riser/tread count — it is a separate structural element, though it is often finished with matching flooring.
Common take-off mistakes
- Ordering the same number of treads as risers instead of one fewer.
- Using a rounded target riser height instead of recalculating the exact figure that divides evenly into total rise.
- Forgetting nosing overhang when sizing tread board width.
- Not adding a waste allowance for solid timber, then coming up short mid-build.
- Treating winder treads as standard-size boards instead of individually templated pieces.
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 many treads and risers do I need for my stairs?
Divide total rise by a target riser height (commonly around 175-200mm/7-8in) and round to a whole number of risers, then subtract one to get the tread count.
Why are there always fewer treads than risers?
Because the top riser of a flight lands on the upper floor, which acts as the final 'tread'. A flight with 13 risers therefore has 12 treads.
How do I calculate the exact riser height?
Divide the measured total rise by the whole number of risers you have chosen. This gives an exact, evenly divided height rather than relying on a rounded target figure.
How much waste allowance should I add when ordering tread and riser timber?
A common allowance is roughly 10-15% for solid timber to cover defects and cutting losses, with somewhat less needed for engineered or MDF stock.
Do open-riser stairs need riser boards?
No, open-riser stairs skip riser boards entirely, though the treads themselves are often made thicker to stay rigid without a riser behind them.
Are winder treads the same size as straight treads?
No. Winder treads are wider at one end than the other and are usually templated and cut individually rather than repeated from a single standard size.
What is nosing overhang and does it affect tread sizing?
Nosing is the tread edge that projects past the riser face, commonly around 20-30mm (0.75-1.25in). It adds to the tread board width beyond the plain going measurement.
Is a landing counted as a tread?
No. A landing is a separate structural element, not part of the tread/riser count, even though it is often finished with matching flooring 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 treads and risersEvery 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.