What is the ideal stair riser height?

Building codes typically allow a maximum riser height of 7.75 inches. For comfort, most builders aim for 7 to 7.5 inches per riser. Going below 4 inches feels awkward and is generally not recommended. Consistency is key — all risers in a staircase should be the same height within 3/8 inch.

How do I calculate the number of stairs I need?

Divide the total rise (floor-to-floor height in inches) by your desired riser height. Round up to the nearest whole number. For example, a 108-inch total rise divided by 7.5 inches gives 14.4, so you'd need 15 risers. Then recalculate the actual riser height: 108 / 15 = 7.2 inches per riser.

What is the standard tread depth for stairs?

Building codes require a minimum tread depth of 10 inches, measured from the nosing to the back of the tread. For comfort, 10 to 11 inches is ideal. The tread depth affects how securely your foot lands on each step — too shallow and the stairs feel unsafe.

What is the 7-11 rule for stairs?

The 7-11 rule is a guideline for comfortable stairs: 7-inch risers and 11-inch treads. Another way to check comfort is the rise + run rule — the riser height plus tread depth should equal 17 to 18 inches. Stairs that follow this ratio feel natural and safe to walk on.

How do I calculate stringer length?

Stringer length is calculated using the Pythagorean theorem: the square root of (total rise squared + total run squared). For example, with a 108-inch rise and 140-inch run, the stringer length is about 177 inches or 14.7 feet. Add 10% extra material for trimming and waste.

What is the maximum stair angle allowed by building code?

Building codes generally limit stair angles to about 37 degrees. The most comfortable range is 30 to 35 degrees. Steeper stairs feel difficult to climb and dangerous to descend. Angles below 20 degrees start to feel more like ramps than stairs.

Staircase Calculator

Calculate risers, treads, stringer length, and stair angle for straight, L-shaped, U-shaped, and spiral staircases. Building code compliant. Free, no signup required.

Total Rise - Floor to Floor Height (in)

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Tread Depth (in)

Stairway Width (in)

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