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In using this calculator it is IMPORTANT that you know and follow the Building Code requirements for stairs in your local area. This Stair Stringer Calculator will let you enter any size stair for planning purposes ONLY. It is NOT an invitation for you to ignore your local Building Code.

This is an easy stair case calculator you can use to determine the rise and run of each step in your stairs and the length of boards you need to buy for your stair stringers. It also gives you the length of the opening to cut in the upper floor of your stairs so you have a minimum amount of head room (see diagram) when using the stairs. (This amount varies per jurisdiction.) If you want to download this stair calculator for field work, here's how.

Numbers can be entered into the stair calculator with a decimal or fraction (i.e. 128.0625 or 128 1/16). (See also How to Build Stairs and How to Cut a Stair Stringer.)

Diagram showing each item mentioned in our Stair Calculator.

  1. Measure the total rise of your stairs (from the surface of the upper floor to the surface of the lower floor). You can use inches, centimeters or millimeters in the stair calculator.
  2. Enter this amount into Stairs Total Rise and set the stair calculator for either inches or centimeters. IMPORTANT NOTE: If you are working in inches, you need to convert any feet measurements into inches. THIS CALCULATOR WILL NOT WORK IF YOU ENTER FEET AND INCHES.
    Examples: WRONG: 8' 2 1/2"      CORRECT: 98 1/2 (just the numbers).
  3. Optional: If you need the length of the stairs Floor Opening in the upper floor then measure the thickness of the upper floor (it might be easier to subtract the ceiling height from the total rise) and enter this into Floor Thickness of the stair calculator. If your physical space for the Total Run is limited you can enter the maximum possible total run of your stairs.
  4. Select a common stair rise-run combination from Simple or enter your own in Custom.
  5. Select the tread material you'll be using or enter its thickness in the space provided. (This is for the measurement of the bottom rise and how far down from the upper floor to secure the top of the stringer.
  6. Press the Calculate button and read the results of the stair calculator in Exact Measurements. NOTE: If any of your settings violates the most common Building Codes then the Calculator will warn you and give you the option of ignoring the warning if it disagrees with the building code in your jurisdiction.
  7. Press the Print Results button at the bottom of the stair calculator. This displays a new page with just the data results and a handy listing of measurements for the stringer markings. A little printer control panel should pop up, but if it does not, go to the File menu at the top of the stair calculator results window. Then click on Print.

How to Use the Stair Calculator

Stair Calculator is set for:                    

Stairs Total Rise


Custom: Rise Run 

This section is optional (see note 3 above)
Floor Thickness
Head Room
Total Run maximum

Tread Thickness:       Custom: Tread

Not recommended: level with upper floor

Exact Measurements of Stairs:

Rise     Run     Rises     Runs

Total run     Length of stringer

Recommended minimum length of stringer board (info)

This section is optional (see note 3 above)
Length of opening in upper floor

(This includes two full-page diagrams of the
stringer giving all measurements and placement.)


Our calculator lets you override this for educational purposes only as we recommend that you comply with the Building Code in your area.


(Ask Dave) (About Dave)

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Hi, I'm Dave Osborne. With over 50 years experience as a journeyman carpenter, foreman and contractor in heavy construction I enjoyed working with apprentices and sharing the tricks of the trade that others shared with me. Now I get emails from Members all over the world and we include many of my answers in our Free Monthly Newsletters. Some of my answers include drawings and instructions specific to a project, but may also answer your questions. I use correct construction terminology, so you can confidently inform your building supply dealers or contractors exactly what you need.


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