Stair Calculator
The stair calculator is used for calculating 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, the
automatic
and
manual
. Click on the [?] icons to determine the best calculator to use for your stairs.
Looking for the Metric (millimeters) version of the Stair Calculator?
Looking for the Metric (millimeters) version of the Stair Calculator?
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 are going to 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 want 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. The top tread would either have a gap on the back side of the tread, or the nose of the tread would not have the same overhang as the other treads. Consider all of the possibilities and think them through, 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, please Contact Us.
Stringer - The stringer is the structural part of a set of stairs. They are cut from 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. It is used to determine the length of 2x12 material required to build 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 vertical rise should be not greater than 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 equal to the number of treads multiplied by the typical Tread Depth [B].
Risers - the Step Height [F] is the typical height of each step. Code states that this should not be greater than 7 3/4 inches (194 mm). In a given run of stairs, the greatest step height and the smallest step height should not vary more than 3/8 inch (9.5 mm). Open risers with openings more then 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 the actual finished height of the first step is the same as the Typical 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 greatest tread depth should not exceed the smallest by more than 3/8 inch (9.5 mm). Typically, a single 2x12 or two 2x6s are used for stair tread material.
Number of Steps (Risers) - The number of risers is not necessarily the same as the number of 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 Position [H] - The stringer position refers to how far below the finished height of the upper landing the stringer will 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 angle is most useful for determining the bevel cut on a stair rail post. It can also be useful for cutting the angle on the top of the stair rail pickets.
Stringer Length - the stringer length calculation is the minimum length of 2x12 material that is required to layout and cut the stringer.
Stairs and Landings - Landings are used to break up runs of stairs. Building code states that the minimum width of a landing should not be less than the width of the flight of stairs that is 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 the Stairs with Landings.
** Note: Building Code information was obtained from the 2021 International Residential Code for One- and Two-Family Dwellings - Section 311 - MEANS OF EGRESS.
Click here for more information on cutting stringers and general stair building.
Mobile Stair Calculator vs. Mobile Friendly Stair Calculator
The Mobile Stair Calculator is available as always on mycarpentry.com, but I urge you to try this very webpage on your mobile or tablet device. I hope you will find it better than my old Mobile Stair Calculator
Click here to access the old Mobile Stair Calculator. Note, that it is designed to work only on a mobile device. If you try to access it from laptop or notebook, it will redirect you back to this page. Please use the contact us form for feedback.
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