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.
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.
|A mobile version of this calculator is available. Click here for more information.|
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 Tread Depth [B] - this is the depth of a single step. This will be the same for all steps (I typically enter a value of 10.5 to 11 inches in this field, because this is a good step depth). 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 Typical Step Height [F] is the desired step height. 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, Total Number of Steps on Stringer, is the total number of steps minus the top step (since the top step on a stair case is typically the landing). 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 Typical Step Height [F] is the height of every step (based on the Total Rise [A] divided by the Number of Steps [D]). 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 tread is installed).
The final result field (Total Run [G]) provides the distance that the stairs will extend out from the deck or landing. This value is determined by the Tread Depth multiplied by the Number of Steps.
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.
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.
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.
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].
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 can put whatever values you want for Tread Depth [B] and Tread Thickness [C].
The best way to explain how this calculator works is through an example. With your mouse, click on the Total Rise [A] input field and enter a value of 48. Enter a value of 10.5 for the Tread Depth [B], 7 for the Number of Steps, and 1.5 for the Tread Thickness. Press the Calculate Stairs button to view the results.
The results are somewhat typical of a standard stair height and depth. Now, suppose you don't have enough room to put a set of stairs with a Total Run [G] of 63 inches. You can do a couple of things to compensate for this. You can reduce the number of steps to 6, and or, you can reduce the Tread Depth [B] from 10.5 to some lower number. After you change the values, just click the Calculate Stairs button again to view the results.
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.
I recently created a mobile version of the automatic calculator. 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.
If you have a little time to test it out and provide some feedback, it would be much appreciated. I plan to expand the capabilities of the mobile carpentry calculator to include all of the other carpentry calculators available on mycarpentry.com.
Click here or on the iPhone image on the left to get started. 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!