# Stair Calculator

The stair calculator calculates stair rise and run, stair angle, stringer length, step height, tread depth, and the number of steps required for a given run of stairs. For convenience and flexibility, this stair stringer calculator comes in two forms: automatic and manual. Click on the [?] icons to determine the best calculator for your stairs.

## Automatic Stair Calculator

Input:
Total Rise [A] (ex: 56.75) (in)
Target Step Height [F] (in)

Stair Results: (fraction) (decimal)
Number of Steps (risers)
Steps on Stringer [D]
Height of First Step [E] (in)
Height of Typical Step [F] (in)
Stringer Placement [H] (in)
Total Run [G] (in)
Stringer Length (in)
Stair/Rail Angle (degrees)

Stringer Mount Type: [?] Standard     Flush

## Manual Stair Calculator

Input:
Total Rise [A] (ex. 56.75) (in)
Total Run [G] (ex. 90.5) (in)
Number of Steps (Risers)

Stair Results: (fraction) (decimal)
Step Height [F] (in)
Steps on Stringer [D]
Height of First Step [E] (in)
Stringer Placement [H] (in)
Stringer Length (in)
Stair/Rail Angle (degrees)

Stringer Mount Type: [?] Standard    Flush

Some results may not meet code requirements

Try adjusting the Total Rise, the Total Run, or the Number of Steps, and re-click

Calculate Stairs

## Stairs with Risers

In most cases, a flight of stairs will require solid risers unless the Total Rise is less than 30 inches (762 mm) OR the typical Step Height is less than 5 1/2 inches (140 mm) (see the Risers section below for related building code requirements).

Adding solid risers to your stairs will not change the results of the Stair Calculator, so long as you properly attach the risers before you add the treads, as shown in the Stairs with Solid Risers and 2x12 Treads diagram below.

Before cutting your stringers, double-check all of your measurements, and carefully plan how you will attach (or not attach) a solid riser at the upper connection point of your stringer. Depending on your design, you may need to adjust the depth of your stringer's top step.

For example, if you are not planning to add a riser to the last rise up to your deck or landing, you may need to subtract the thickness of one riser from the calculated Tread Depth [B] on the top step of the stringers. Using the diagram below, picture the top step without the last riser installed. Without the riser, the last tread would either have a gap on the back side or the nose of the tread would not have the same overhang as the other treads. Consider all of the possibilities before cutting your first stringer.

## Stair Calculator Results and Related Building Codes**

The information below explains the stair calculator results in more detail and provides related **building code information. If you have any questions, Contact Us.

Stringer - The stringer is the structural part of a set of stairs. They are 2x12s (or larger) material - the uncut portion of the stringer should not be less than 5 inches (127 mm) (see diagrams below). In a set of stairs 36 inches wide, there are typically three stringers (one on each end and one in the middle). The Stringer Length is the tip-to-tip length of the cut stringer. The Stringer Length value is the minimum length of 2x12 material required to lay out the stair stringer.

Total Rise [A] - The Total Rise of a flight of stairs is the vertical rise between the bottom of the first step and the top of the finished landing. The Total Rise [A] should not exceed 151 inches (3835 mm) between landings or floor levels.

Total Run [G] - The Total Run is the horizontal length of a stair stringer. It is the Number of Steps [D] (on the stringer) multiplied by the Tread Depth [B].

Risers - The Step Height [F] is the typical height of each step. The Building Code states it should not exceed 7 3/4 inches (194 mm). In a given run of stairs, the Step Heights should not vary more than 3/8 inch (9.5 mm). Open risers with openings more than 30 inches (762 mm) vertical to the floor should not permit the passage of a 4-inch-diameter (102 mm) sphere.

Height of First Step [E] - The actual finished height of the first step is the same as the Step Height [F], but when you cut the stair stringer, the First Step Height [E] is always the Step Height [F] minus the Tread Thickness [C].

Treads - The Tread Depth [B] should not be less than 10 inches (254 mm). In a given run of stairs, the Tread Depth [B] should not vary by more than 3/8 inch (9.5 mm). Typically, stair treads are either a single 2x12 or two 2x6s.

Number of Steps (Risers) - The number of risers is not necessarily the same as the Steps on Stringer [D]. If the Stinger Mount Type is Flush, then the number of risers is the same as the number of steps. If the Stringer Mount Type is Standard, the number of risers will be one more than the number of Steps on Stringer [D].

Stringer Placement [H] - Stringer Placement refers to how far below the Finished Height of the upper landing the stringer should be attached.

Headroom - The headroom should not be less than 6' 8" (2032 mm), measured vertically from the stair tread nosing to the nearest ceiling object.

Stair/Rail Angle - The Stair/Rail Angle is the bevel cut on a stair rail post. It can also be the angle on the top of the stair rail balusters attached to the rail.

Stringer Length - The Stringer Length calculation is the minimum length of 2x12 material required to lay out and cut the stringer.

Stairs and Landings - Landings break up long runs of stairs (where the Total Rise [A] is more than 151 inches). The building code further states that the minimum width of a landing should not be less than the width of the flight of stairs served. **"Where the stairway has a straight run, the depth in the direction of travel shall be not less than 36 inches (914 mm)." For additional information, check out Stairs with Landings.

** Note: For building code information related to stair construction, visit 2021 International Residential Code for One- and Two-Family Dwellings - Section 311 - MEANS OF EGRESS.

## Mobile Stair Calculator vs. Mobile Friendly Stair Calculator

The old Mobile Stair Calculator is available now on mycarpentry.com but will be deprecated soon. I urge you to try the Stair Calculator on this webpage on your mobile or tablet device. You will find its responsive design works as well on mobile devices as on a desktop computer.