Minimum stair tread depth UK: how to measure the going

Minimum stair tread depth UK: start with the right measurement

When someone asks for the minimum stair tread depth UK rules allow, they usually mean the minimum going. Going is the horizontal distance between corresponding points on consecutive steps, commonly measured from one nosing to the next. It is not necessarily the full front-to-back depth of a physical tread, because a projecting nosing can add depth without adding the same amount of going. Record both dimensions if you are ordering replacement treads, but use going for the regulatory check.

There is no single stair dimension that applies to every staircase throughout the UK. Building regulations differ between England, Wales, Scotland and Northern Ireland, and requirements can also depend on the stair's purpose and the work proposed. In England, Approved Document K gives a minimum going of 220 mm for a private stair. Treat that figure as a starting point for checking an English private stair, not as permission to use 220 mm for every stair or every location.

• Write down the property's nation before looking up guidance.
• Identify whether the stair serves one dwelling or has another use.
• Label tread depth and horizontal going separately on your sketch.

Establish which guidance applies

First decide whether you are checking an existing staircase, designing a replacement, or altering the stair during building work. An older stair may have been built under different requirements; measuring it does not establish whether it was lawful when installed or whether proposed work is compliant now. Note whether the stair is inside a single dwelling, serves a shared area, or provides another form of access. These distinctions matter before you compare a number with a published table.

For work in England, open the current edition of Approved Document K from GOV.UK and find the stair category that matches your project. Its guidance for private stairs includes a going range of 220 mm to 300 mm, a rise range of 150 mm to 220 mm, and a maximum pitch of 42 degrees. Other stair categories have different provisions, so do not carry the private-stair minimum across to a communal or public stair. For a property elsewhere in the UK, consult that nation's current building standards guidance and your building control body rather than assuming the English table applies.

Measure every going in millimetres

Use a rigid tape measure or rule, a pencil and a simple side-view sketch. Mark the front edge or nosing of one step and the equivalent point on the next, then measure the horizontal distance between them. Hold the measure level: a diagonal measurement along the sloping line of the stair will overstate the going. If carpets or trims obscure the edges, note that limitation and expose a reliable reference point before using the figures for design.

Start at the bottom and give each step a number so that measurements can be traced back to their position. Measure each going separately rather than multiplying one sample measurement by the number of steps. Record the smallest reading, the largest reading and any step whose shape differs, including steps near a landing or turn. If a tread is tapered or the stair winds, use the relevant method in the applicable national guidance; a measurement at an arbitrary point across the tread may be misleading.

• Measure horizontally between equivalent points on successive steps.
• Record each result in mm beside its step number.
• Flag coverings, damaged nosings or tapered steps that affect accuracy.

Check rise and the available space

Going is only one part of a usable stair. Measure each rise vertically between the finished surfaces of consecutive steps, including the finished floor and landing where relevant. For an English private stair, compare those readings with the 150 mm to 220 mm rise range in Approved Document K. Finished flooring matters: adding a thick floor covering at one end can change the effective first or last rise.

Check the proposed layout before buying timber treads, nosings or carpet. Count the rises between finished floor levels, then check that the available horizontal space can accommodate the planned goings and landings. For a straight flight with equal goings, multiplying the going by the number of going intervals gives a useful initial horizontal layout check. Draw the actual top and bottom connections as well, because the number of goings is not automatically the same as the number of rises.

Compare the readings and investigate exceptions

Put your measurements beside the figures for the correct stair category and nation. On an English private stair, a measured going below 220 mm falls below the minimum going stated in Approved Document K's guidance. A reading of exactly 220 mm leaves no allowance for measurement uncertainty or differences between a drawing and finished construction. Re-measure any borderline result from clear, consistent reference points before making a decision.

Review the whole flight rather than reporting only its average. A mix of goings can reveal a construction error, an altered landing or a measurement taken from inconsistent points. Note any tapered steps, projecting nosings, worn edges or floor finishes that need a closer check under the relevant guidance. If you are planning building work or cannot confidently classify the stair, take the dimensioned sketch to the designer or building control body before ordering components.

• Compare the smallest measured going with the applicable minimum.
• Check every rise and the proposed pitch, not just the going.
• Investigate unusual steps and measurements close to a limit.

Keep a record that someone else can verify

Make a one-page record showing the property location, date, stair use and whether the figures describe an existing or proposed stair. Include a side-view sketch with step numbers, the measured goings and rises, and the finished floor levels used as references. Photograph the stair from the side and photograph any obstructed or unusual step. These records make it easier for a joiner, designer or building control professional to check the same points.

Write down the title and edition date of the national guidance you consulted, along with the stair category you selected. If you are replacing treads, separately record the physical tread depth, nosing projection, width and intended finish so that ordering dimensions are not mistaken for going. Ask the person responsible for the design to confirm the full stair arrangement where regulations apply. Keep the confirmed drawing and measurements with the rest of the property's alteration records.

Final verification checklist

Before relying on a minimum figure, confirm the property's nation, the nature of the work and the stair's use. Check that the guidance you opened is current for that location and that you are reading the correct stair category. For an English private stair, verify the measured going against the 220 mm minimum in Approved Document K. Do not use that figure as a substitute for checking a stair in another UK nation.

Finally, revisit the staircase with your numbered sketch and repeat any reading that appears unusually small or large. Check that measurements run horizontally between equivalent points and that rises use finished surfaces. Confirm that landings, pitch and any tapered steps have been considered in the overall design. Keep the verified measurements and seek project-specific advice before work proceeds if any reading or classification remains uncertain.

• Correct UK nation, work type and stair category identified.
• Every going and rise measured in mm from consistent points.
• Smallest going and any unusual step checked against current guidance.
• Sketch, photographs and guidance edition retained with the project records.

Scope and limitations

This note helps householders organise measurements and understand the calculation. It does not replace an on-site decision by a designer, installer, contractor, or manufacturer. Fabrication, structure, electrical work, gas, waterproofing, and personal safety require suitably qualified verification.