Stair Calculator

Key Stair Terminology Explained

Tread (Run)

The tread, also called the run, is the flat surface you step on. It’s measured from the front edge of the tread (including any overhang or nosing) to the vertical part behind it (riser). When calculating the total stair run, don’t count the last tread or any part of the nosing overhang more than once.

• Recommended Minimum Tread Length: 10 inches (25.4 cm)

Riser (Rise)

The riser is the vertical part between two treads. The rise refers to the distance from the top of one tread to the top of the next tread—not just the riser board height itself. When calculating the total number of steps, count the risers, not the treads.

• Recommended Maximum Riser Height: 7.75 inches (19.7 cm)

Nosing

Nosing is the projecting edge of a tread that extends beyond the riser below it. While not required in all stairs, nosing provides added safety by increasing the surface area for each step.

• Recommended Nosing Size: Between 0.75 inches (1.9 cm) and 1.25 inches (3.2 cm)

Headroom

Headroom refers to the vertical space from a tread to the ceiling above. Adequate headroom ensures people can comfortably use the stairs and safely move large items up or down.

• Recommended Minimum Headroom Clearance: 6 feet 8 inches (203.2 cm)

Stair Width

Stair width is the measurement from side to side across the tread, excluding handrails. Unlike other shapes where length is greater, stair width is typically the longer dimension.

• Recommended Minimum Stair Width: 36 inches (91.44 cm)

Handrails and Guardrails for Stair Safety

Handrails

A handrail runs along the incline of the stairs and provides support while ascending or descending. It’s a required safety feature for most staircases.

Guardrails (or Guards)

Guards prevent people from falling off elevated walking surfaces. These can include traditional rails, walls, or even benches that meet safety requirements.

• Required for stairs with a rise over 30 inches

• Minimum Guard Height: 34 inches (86.36 cm)

• Handrail Height Range: 34–38 inches (86.36–96.52 cm)

• Handrail Diameter: Between 1.25 inches (3.18 cm) and 2.675 inches (6.79 cm)

What is a Stair Stringer?

A stringer is the structural support that holds up the stair treads and risers. Most staircases have three stringers—one on each side and one in the center. Depending on the design, stringers may be exposed or hidden and can be cut to match the shape of the stairs or left solid for a cleaner appearance.

Fraction to Decimal Conversion Chart