Stair Calculator

The stair calculator below can be used for calculating the rise and run of a set of stairs, as well as other important details of stringer layout and design.  This stair stringer calculator comes in two forms, the automatic and manual.

Automatic Stair Calculator

Input: Auto Calculator Help
Total Rise [A] (ex: 56.75) (in)
Target Step Height [F] (in)  
Tread Thickness [C] (in)
Tread Depth [B] (in)  

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

Stair Section

Automatic Calculator Help

The Total Rise [A] is the finished height of your landing or deck.  The Target Step Height [F], is the height that you would like your steps to be.  The automatic calculator will try to design your stair stringer as close to the target height as possible, while maintaining a common step height. 

For instance, if you have a Total Rise [A] of 21 inches, and you have selected six inches as your Target Step Height, the calculator will determine that 3 steps at 7 inches is best, since 6 inches does not divide equally in 21 inches.  Since 21 divided by 6 equals 3.5, therefore maintaining a 6 inch step would mean that you would have to build three steps at 6 inches and one step at 3 inches.  Poor Design. 

Obviously, unless things work out perfectly (and they rarely do), the Height of typical step [F] won't match the Target Step Height that you specify.  This is because the number of steps must be a whole number.  You'll see what I mean when you use the calculator.  Try changing the target values and compare the results.

Using the Automatic Calculator

Mobile Stair Calculator A mobile version of this calculator is available.  Click here for more information.

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Manual Stair Calculator

Input (enter decimal values) Manual Calculator Help
Total Rise [A] (in)  
Total Run [G] (in)  
Number of Steps (Risers) (qty)
Thickness of Tread Material [C] (in)  

Results (stringer layout and dimensions) (fraction) (decimal)
Step Height [F] (in)
Tread Depth (step run) [B] (in)
Total Number of Steps (Treads) [D] (qty)
Height of First Step [E] (in)
Position of Stringer on Landing [H] (in)
Stringer Length (in)
Stair/Rail Angle (degrees)

Stair Section

Manual Calculator Help

Input - On the Input section, enter the Total Rise [A] of the deck or landing to which the stairs will be built (this is the total finished height of the deck or landing).  Next, enter the Total Run [G] - this is the total horizontal space that you have available for your stairs.  The third input field, Number of Steps [D], is a number that you arbitrarily input to test various rise/run scenarios.  You will most likely change this value a few times until the  Step Height [F] and Step Run [B] are the suitable for your needs.  The last input field (Tread Thickness [C]) is used to calculate the height of the first step on the stringer. 

Note: Any of the input fields can be changed after you press the Calculate button so that you can test various scenarios and observe the results.

Results - The first result field, Step Height, is the height of a typical step.  The second field, Step Run [B] is the amount of total run per step, based on the total run divided by the number of treads.  The second field, Height of the First Step [E], is automatically calculated by subtracting the Tread Material Thickness [C] from the Typical Step Height [F]

The third result field, Number of Treads on Stringer, is always the total number or steps minus 1.  The Height of the first step [E], is the height of a typical step minus the thickness of the tread material.  The next result field, Position of Stringer on Landing [H], is the distance between the finished height of the landing to the top step on the stringer (before the top tread is installed). 

Using the Manual Calculator

Back to the Auto Calculator

Using the Automatic Stair Calculator

The automatic stair calculator is most useful in situations where the ground or slab is level between the top step and the bottom step (Total Run [G]).  It is called the automatic stair calculator because, if you accept the pre-selected default values, you only have to enter the Total Rise [A] (see the Stair Stringer Diagram).  The automatic calculator does the rest of the computations for you.

 It automatically calculates the values that you need in order to layout and cut your first stair stringer.  The first stair stringer is typically used as a pattern for the remaining stringers. 

The calculated results are based on the input of Total Rise [A] plus three pre-selected variables (target step height, tread thickness, and tread depth).  You can change the pre-selected values as needed by selecting one of the other values from the drop-down list boxes.  Keep in mind that the pre-selected values are the most common for residential stairs.

Getting Started

Select the Total Rise [A] input field (shown in green).  Enter a value (less than 1200 inches) and press the Calculate Stairs button.  That's all there is to it! 

If you want to change the value of one of the other pre-defined input fields, just click the down-arrow and select one of the other values, then click the Calculate Stairs button again.

For more detailed help, click the Auto Calculator Help button located on the top right corner of the calculator.

Stair Stringer Profile
Stair Stringer Diagram

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Which calculator should I use?

For most interior stair building scenarios, it is best to use the automatic stair calculator.  For instance, if you are building stairs inside of a building, where the slab is level and the location of the bottom step in the room is not critical, the automatic calculator is the easiest to use, since you only have to input one value (the Total Rise [A]) to calculate everything you need to cut your stringers.

Use the manual stair calculator in situations where the ground is uneven between the bottom step and the top step (see the diagram below), or if you need to build a ladder type stair that might be located in a confined space where typical step dimensions would not fit.

Stair Building on Uneven Terrain
Building Stairs on Uneven Ground

When you are building stairs on uneven ground, as shown in the diagram above, there are several things to consider.  For instance, if you are trying to determine the Total Rise [A] of your stairs, you must have some idea of where the bottom step will land [J].

There are two factors that will determine this.  The Number of Steps and the Tread Depth [B]The number of steps times the tread depth will give you the location of the bottom step [J].  Depending on how far away your bottom step is from the landing, you may have to use a transit level to determine the Total Rise [A].

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Using the Manual Stair Calculator

This purpose of this calculator is to design stairs for conditions where standard step heights and depths will produce a set of stairs that won't fit in the space that you have to work with. 

This Manual Stair Calculator is slightly more difficult to use, but allows for greater flexibility than the Automatic Stair Calculator.  For instance, you control the Total Rise [A], Total Run [G], Number or Steps, and Tread Thickness [C]

Getting Started

The best way to explain how this calculator works is by example.  Click on the Total Rise [A] input field and enter a value of 48.  Enter a value of 63 for the Total Run [G].  Enter 7 for the Number of Steps, and 1.5 for the Tread Thickness.  Press the Calculate Stairs button to view the results.

If you don't like the Step Rise and Run results, you can change the Number of Steps value and recalculate the results.  You can keep changing the Number of Steps until you achieve the desired results.

Back to the Manual Calculator

For reference, refer to the Stair Stringer Profile diagram at the top of the page. Click here for more information on cutting stringers and general stair building.

Mobile Stair Calculator

Mobile Stair CalculatorI am working on a new mobile version of the automatic calculator, but I will keep the current version available until the new one is finished and tested. 

The current mobile version works best when viewed in the "portrait" position.  I tested it on an iPhone 3g and an iPhone 4s, but haven't had the opportunity to test it on any Android or Windows Mobile operating systems.

 I plan to expand the capabilities of the mobile carpentry calculator to include all of the other carpentry calculators available on

Click here or on the iPhone image on the left to access the 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.

~ Thank you!


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