Theoretical values for estimating only. Confirm against the mill certificate or a stamped calculation before ordering or fabricating.
You cannot have a fractional riser, so the design job is to round to a whole number and then accept the riser height that results. This calculator does that rounding for you and shows the consequence.
Round the riser count, then fix the height
Divide the total rise by a target riser height and round to the nearest whole number. The actual riser height is then total rise ÷ that number — it will rarely match your target exactly, and that is fine as long as every riser is the same.
Treads are one fewer than risers
The top riser steps onto the finished floor, so a flight of 16 risers has 15 treads. Total run = 15 × tread depth.
Anti-slip treads on industrial stairs
Industrial and offshore stairs normally use open or punched anti-slip treads rather than a plain plate nosing. These are specified by tread depth, width and the fixing centres of the stringer.
Getting the material list right
Once the riser count and tread depth are fixed, the tread count and the stringer length follow — which is everything needed to price a stair package.
Frequently asked questions
How many treads and risers do I need?
Divide the total rise by about 180 mm and round to get the riser count. A 2,800 mm rise gives 16 risers; treads are always one fewer, so 15.
How tall should each riser be?
Between 100 mm and 200 mm. 175–190 mm is the usual comfortable range for industrial and commercial stairs.
What is the minimum tread depth?
250 mm (about 10 in) under most codes, with 280 mm typical for industrial access stairs where boots and tools are carried.
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