🪜Stair Slope & Tread Calculator

Enter total rise and number of steps to calculate riser height, tread depth, slope angle, and code compliance.

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Stair Slope & Tread Spacing Calculator Guide

Enter the total rise (floor-to-floor height) and the number of risers. Optionally add the total run to calculate actual tread depth. The calculator checks Blondel's rule and IRC/IBC residential code compliance.

Blondel's Rule

French architect Blondel established that 2 × Riser + Tread should equal approximately 24–25 inches (63 cm). This ratio aligns with a comfortable human stride. For example, a 7-inch riser pairs ideally with an 11-inch tread (2×7+11=25).

US Building Code (IRC Residential)

IRC 2021: Maximum riser height 7.75 in (196mm), minimum tread depth 10 in (254mm), and headroom 6 ft 8 in (2032mm). Commercial stairs (IBC) require max riser 7 in and min tread 11 in. Always check local amendments.

Frequently Asked Questions

What is a comfortable stair slope for residential use?

30–38° is the comfortable range. Shallower than 25° wastes space; steeper than 45° is difficult and may not meet code for main interior stairs.

How do I find the number of steps for a given rise?

Divide the total floor-to-floor height by the desired riser height. For example, 110 in ÷ 7 in = 15.7, so use 16 risers at 6.875 in each.