Calculate Unit Run and Total Run

What happens in this clip

Now, determine the 'unit run' (the depth of each step) and the 'total run' (the overall horizontal distance the stairs will cover). A golden rule for comfortable stairs is that the sum of the unit rise and unit run should be between 17 to 18 inches. Given a unit rise of 7.25 inches, a unit run of approximately 10 to 10.5 inches would be suitable (e.g., 10.25 inches). To find the total run, count the number of rises determined in the previous step (e.g., 8 rises). The number of treads (or unit runs) will typically be one less than the number of rises. So, for 8 rises, there will be 7 runs. Multiply the unit run by the number of runs to get the total run. For example, 10.25 inches (unit run) * 7 (runs) = 71.75 inches total run.

Goal: Determine the depth of each step and the overall horizontal length of the stairs.

What's used

Tools

• Calculator
• Marker
• Whiteboard

About the full video

This project provides a comprehensive guide on calculating and building a simple set of stairs. It covers the essential mathematics behind determining unit rise and run, understanding crucial adjustments for tread thickness, and the practical application of a framing square for laying out stringers. The video concludes with instructions on cutting and assembling the stair components.

Step 6 of 6: Calculate Actual Tread Run

Using the total run and the number of treads, divide the total run by the number of treads to calculate the precise depth of each individual tread. For the example of a 120-inch total run and 12 treads, the actual tread run would be 120 inches / 12 treads = 10 inches per tread.

Open this step in the guide

Every video in How to Measure Stair Rise and Run

1. Step 1: Determine Total Rise

   • 0:04–0:30 Measure Total Rise
   • 2:54–4:34 Determine the Total Rise
   • 0:54–1:25 Calculate Final Total Rise

2. Step 2: Calculate Ideal Riser Height

   • 0:29–1:07 Calculate Rise and Run
   • 4:32–5:10 Calculate Individual Riser Height
   • 0:28–1:03 Calculate Approximate Number of Risers

3. Step 3: Determine Actual Riser Height

   • 4:32–5:10 Calculate Individual Riser Height
   • 1:03–1:44 Calculate Riser Height (Option 1)
   • 0:28–1:03 Calculate Approximate Number of Risers

4. Step 4: Determine Number of Treads (Steps)

   • 0:54–1:13 Determine Number of Treads
   • 3:54–5:04 Calculate the Number of Treads and Understand the Logic
   • 8:59–9:54 Calculate Number of Risers and Treads

5. Step 5: Measure Total Run

   • 1:31–2:57 Calculate Unit Run and Total Run
   • 1:13–1:29 Calculate Total Run
   • 9:54–10:28 Determine Tread Run and Total Run

6. Step 6: Calculate Actual Tread Run

   • 0:29–1:07 Calculate Rise and Run
   • 1:31–2:57 Calculate Unit Run and Total Run (this video)
   • 10:55–11:31 Calculate Overall Run (Treads)