Stair Calculator

Start with total rise (the vertical distance from finished floor to finished floor). Pick a preferred riser height. The number of risers is total rise divided by preferred riser, rounded to the nearest whole number. The actual riser height is total rise divided by that number of risers. The number of treads is one less than the number of risers for most layouts because the top landing replaces the top tread. Total run is the number of treads multiplied by the tread depth.

Residential stairs commonly target a riser height around 7 to 7.75 inches. Going higher than that gets steep and uncomfortable; going lower gets long and uses more floor space. Local building codes often set a maximum riser height; check yours before building.

Tread depths of 10 to 11 inches are common for residential interior stairs. Deeper treads (11 to 12 inches) are easier to walk on but use more floor length. Shallower treads (under 10 inches) are usually only acceptable on space-saving or alternating-tread stairs. Local code typically sets a minimum tread depth.

Picture a flight of stairs against a wall. Every step has a vertical face (the riser) and a horizontal face (the tread). The very top tread is the floor of the upper level, so it does not count as a stair tread. That leaves one fewer tread than riser. Some open or floating stair designs handle the top step differently; this calculator follows the standard residential layout.

Stair angle is the arctangent of total rise divided by total run. The calculator computes that angle in degrees using your inputs. The angle is a rough planning figure; comfortable residential stairs commonly land in the low-to-mid 30s. Local code may cap stair angle near 38 degrees.

Use it for planning only. Stair codes, riser and tread limits, headroom requirements, handrail rules, and inspection requirements vary by location and project type. Confirm the final design with your local building code and, when needed, a qualified professional before building.