Workshop journal · published by Heritage & Decorative Timber Products · updated 8 October 2026

How to Measure Outdoor Stairs Before Ordering a Timber Stair Kit

Quick answer

Measure vertically from the finished landing level to the finished top of the deck, then record the available run and clear stair width. Use those measurements to check tread count; do not choose the number of treads by appearance alone.

Outdoor stairs are easy to underestimate. From the garden, a deck may look as though it needs six or seven treads, but the correct stair layout begins with a vertical measurement, not a visual guess. A small measuring error at the start can change the tread count, the stringer length and where the stair lands.

This guide explains what to measure before discussing a timber stair kit. It is a planning guide rather than engineering or building-approval advice; confirm the finished design and local requirements with the person responsible for the project.

Start with the finished ground-to-deck height

Measure vertically from the finished landing level to the finished top of the deck. “Finished” matters. If paving, concrete, decking or landscaping is still to be installed, allow for that final surface rather than measuring from temporary soil or framing.

Keep the tape vertical. Do not measure diagonally down the intended line of the stairs, because that produces the sloping stair length rather than the rise. Take the measurement at both sides of the proposed stair. If the ground falls away, record both figures and decide how the landing will be formed.

Use tread count as a check, not the first measurement

Once the vertical height is known, you can compare possible tread counts. Karem Woodcraft customers often think in terms of “seven-tread stairs” or “ten-tread stairs”, which is useful when ordering, but the tread count still has to suit the actual rise.

The Heritage Decorative Timber stair calculator provides two useful starting methods: enter the ground-to-deck height, or select a tread count using the standard 165 mm rise planning option. It then gives a clearer basis for discussing LOSP pine, Merbau or other available stair-kit choices.

Measure the available run and clear width

Stairs need room in front of the deck. Measure from the deck edge to the point where the stair may finish, allowing for the landing and for gates, paths, garden beds, downpipes and doors. Photograph the whole area rather than only the deck edge.

Next, measure the clear width available for the flight. Note whether the width is between walls or posts, or whether one or both sides are open. Record nearby handrails, balustrades and structural posts because they may affect how the stringers and finished stair relate to the deck.

What to send when requesting a stair quote

Finished ground-to-deck height in millimetres
Preferred tread count, if you already have one
Available horizontal space
Required stair width
Photographs taken square-on and from each side
Your suburb or postcode for pickup or freight planning
Your preferred material, if known

A quick sketch with the main measurements is often more useful than a long written description. Mark which surfaces are finished and which are still to be built.

Common measuring mistakes

The most common mistakes are measuring to the underside of the deck instead of its finished top, measuring before paving is installed, assuming the ground is level, and choosing tread count purely by appearance. Another is forgetting that the bottom of the flight needs a suitable landing rather than finishing in loose soil.

Good stair planning does not begin with a product code. It begins with one reliable vertical measurement, a realistic landing position and clear photographs. With those details, the stair-kit conversation becomes much faster and far less dependent on guesswork.