Outdoor stair planning
How to measure the space for outdoor timber stairs
Prepare three measurements before enquiring about a stair kit: the height between finished surfaces, the horizontal space available and the width you need. Add a labelled sketch and photographs so the numbers describe the same project.
You do not need to turn an initial enquiry into a construction drawing. The aim is to give the team a clear starting point and identify what still needs checking. If a surface or level will change, record that instead of presenting an uncertain measurement as final.
1. Identify the finished lower and upper surfaces
The total rise is the vertical distance the stairs must climb. Identify the intended walking surface at the bottom and the intended surface at the top. Paving, decking or other finishes that are still to be installed can change those levels.
A diagonal measurement along an existing stair is not the total rise. Label the vertical measurement explicitly on your sketch. If your builder has already established finished levels, use that information and show where it came from.
2. Record the horizontal space available
Measure the space the flight can occupy in plan, rather than only the length of the old stairs. Show the deck or landing edge, nearby walls, paths, doors and other features that affect the position. Include photographs looking across the space, not just straight at the stairs.
Distinguish available space from the projection of a proposed flight. One describes the site; the other is the result of a particular layout. Keeping both labels clear makes it easier to compare calculator results with the real location.
3. Measure width across the flight
Width is measured across the stairs, from one side towards the other. It cannot be read from a side-view sketch alone. Mark where the width was measured, especially if a handrail, post or wall limits the usable space.
For replacement stairs, note which surrounding components will remain. An old tread length by itself may not describe the new flight or the space needed for its complete assembly. Send photographs of the existing connections for assessment.
4. Keep the terminology clear
A riser describes a vertical step between levels; a tread is a walking surface. The upper landing can form the final walking surface, so the number of separate treads is not always the number of rises. “Going” describes horizontal spacing in the stair layout and should not be assumed to equal the full depth of a tread board.
Use the stair calculator to explore a preliminary arrangement. Check its assumptions and units before copying the result into an enquiry. It does not assess structural supports, handrails or the complete site.
Send a brief that is easy to review
- Project location and whether the stairs are new or replacements.
- Finished total rise, available horizontal space and required width in millimetres.
- A labelled sketch, photographs and any existing project drawings.
- Notes about unfinished surfaces and components that will remain.
- Your preferred stair kit range and questions still to resolve.
Send your measurements for a quote. Confirm the final layout and installation requirements with the appropriate project professional before ordering. For indoor work, see internal stairs.