Stair Stringer Calculator

How this calculator works

This calculator estimates stair risers, treads, total run, stringer length, angle, and optional total stringer length for planning. It supports metric and imperial dimensions.

Stairs are safety-critical. Dimensions, handrails, landings, headroom, tread nosing, and safety rules vary by location, so this page does not claim code compliance.

Formula

• Riser count = round(total rise / target riser height).
• Actual riser height = total rise / riser count.
• Tread count = riser count - 1.
• Total run = tread count x tread depth.
• Stringer length = square root of (total rise squared + total run squared).
• Stair angle = arctangent(total rise / total run), converted to degrees.

Worked example

For a total rise of 2800 mm and a target riser height of 175 mm, riser count is 16 and actual riser height is 175 mm.

With a 270 mm tread depth, tread count is 15 and total run is 4050 mm. Stringer length is approximately 4.92 m.

Common mistakes

• Using unfinished floor heights instead of finished surface-to-surface rise.
• Forgetting that tread count is usually one less than riser count.
• Ignoring headroom, landings, handrails, tread nosing, and safety requirements.
• Cutting stringers before checking the real site conditions and material.

FAQs