Stair Handrail Calculator

Worked example

With these inputs:

• Number of risers: 9 risers
• Riser height: 7.5 in
• Tread depth (nosing to nosing): 10 in
• Extensions: None — rail stops at the top and bottom nosings (IRC)
• Handrails: One side

Length follows the nosing line from the top nosing to the bottom one. IRC R311.7.8: a handrail on at least one side of any flight with four or more risers, 34–38 in above the nosings, continuous for the full flight; graspable (R311.7.8.5). ADA 505.10 extensions apply to public and accessible stairs. Add the returns or end caps your rail system uses.

How it works

A stair handrail runs parallel to the line of the tread nosings, so its length is the hypotenuse of a triangle whose sides are the total tread run and the total rise between the top and bottom nosings. This works that out from your riser count, riser height and tread depth, adds the top and bottom extensions if you build to the ADA Standards, and picks the stock length that does it in one piece.

Frequently asked questions

How do you calculate handrail length for stairs?

Treat it as a right triangle. The horizontal side is the number of treads times the tread depth, the vertical side is the number of treads times the riser height, and the handrail is the hypotenuse. Nine risers at 7.5 in with 10 in treads is eight treads: 80 in across and 60 in up, so the rail is exactly 100 in, or 8 ft 4 in.

What height should a stair handrail be?

Between 34 and 38 in, measured straight up from the line of the tread nosings. That range is in both the IRC (R311.7.8.1) and the ADA Standards (505.4). Deck guards are a different thing: an open side more than 30 in above the ground needs a 36 in guard at a house.

How many steps before you need a handrail?

Under the IRC, any flight with four or more risers needs a handrail on at least one side. Three risers or fewer need none by code, though a rail still helps anyone unsteady on their feet. Public and commercial stairs follow the IBC and ADA, which want rails on both sides.

Do handrails need to extend past the stairs?

At a house under the IRC, no: the rail must run the full length of the flight, from above the top riser to above the bottom one. The ADA Standards (505.10) add a 12 in horizontal extension at the top and a sloped extension one tread deep at the bottom, which the calculator includes when you choose ADA.

What angle is a stair handrail?

The same as the stair's pitch: the arctangent of riser height divided by tread depth. A 7.5 in riser on a 10 in tread gives 36.9°. A 7¾ in riser on a 10 in tread, the steepest the IRC allows, gives 37.8°.