For stairs with nosing, the tread depth is equal to the run of each step plus the nosing depth.

We will need to get the tread depth of the first landing, and then get the sum of the runs for all succeeding step landings.

Our instructions assume uniform measurements for each step.

Step 1: Measure the nosing of the first step landing

Step 2: Get the tread depth of the first step landing (include the nosing in the measurement)

Step 3: Measure the tread depth of the second step landing

Step 4: Subtract the nosing from Step 1 from the measurement you got in Step 3. This is the run for this step landing.

Step 5: Repeat Steps 3 and 4 until you have the run for each succeeding step landing

Step 6: Add the tread depth of the first step landing (from Step 2) to the sum of the runs of the second step landing onwards (Step 4 and 5)

In this example, the first step is 12 inches deep and the succeeding steps are 11 inches deep. Together, the total distance is 45 inches or 3.75 feet.