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 7: Determine the Total Run

Multiply the number of treads (from Step 5) by the desired tread depth. A common tread depth is 10 to 11 inches, but this can vary. Ensure the tread depth is consistent and meets local code requirements. For example, if you have 13 treads and a desired tread depth of 10 inches, the total run is 13 * 10 = 130 inches.

Open this step in the guide

Every video in How to Calculate How Many Stairs You Need

1. Step 1: Measure the Total Rise

   • 0:15–0:29 Measure Total Rise
   • 0:01–0:28 Measure Total Vertical Rise
   • 0:17–0:31 Measure Total Rise

2. Step 2: Determine the Ideal Riser Height

   • 1:03–1:44 Calculate Riser Height (Option 1)
   • 1:44–2:33 Calculate Riser Height (Option 2) and Verify Code Compliance
   • 4:32–5:10 Calculate Individual Riser Height

3. Step 3: Calculate the Number of Risers

   • 0:32–0:54 Calculate Number of Risers
   • 8:59–9:54 Calculate Number of Risers and Treads
   • 7:42–8:55 Calculate Number of Risers

4. Step 4: Recalculate Actual Riser Height

   • 1:03–1:44 Calculate Riser Height (Option 1)
   • 4:32–5:10 Calculate Individual Riser Height
   • 1:44–2:33 Calculate Riser Height (Option 2) and Verify Code Compliance

5. Step 5: Calculate the Number of Treads

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

6. Step 6: Determine the Total Run

   • 1:13–1:29 Calculate Total Run
   • 1:31–2:57 Calculate Unit Run and Total Run (this video)
   • 6:51–8:30 Calculate Total Run

7. Step 7: Calculate Tread Depth

   • 2:05–2:24 Calculate Individual Riser Height & Tread Depth
   • 9:54–10:28 Determine Tread Run and Total Run
   • 8:50–10:30 Calculate Risers, Treads, and Total Run