How to calculate Stair Rise and Run

1.) Determine total rise (finish floor height to finish floor height) in Inches

2.) Find # of Risers- Divide total rise by 7 (ideal riser height)

3.) Take the answer from step two and Round up or down to the nearest whole

number (14, 15, 16 etc.) since we cant have 14.3 risers, etc.

4.) Divide total rise (in inches) by the whole number of risers that you found in

step 3. This gives you the total rise of each stair.

5.) Find the number of Treads required- there is always one less tread than the

total number of risers. Ex. 14 risers = 13 treads.

6.) Figure total run by multiplying ideal tread width x # of treads.

7.) Adjust Run/Tread width as needed to meet the needs of your floor plan but

remember to stay within the code allowed tread width min. of 9

Example Formula:

Step 1. Determine the total rise in inches finished floor to finished floor

inch plywood

9 floor joist

3 top plates

104 5/8 studs

+_1 bottom plate_________________

119.125 inches (119 1/8 ) Total Rise

Step 2. Find the total number of risers required.

Divide total rise by 7

119.125 / 7 =17.018

Step 3. Round the answer you got in step 2 up or down to nearest whole number

= 17 risers

Step 4. Divide total rise (in inches) by this number

119.125 / 17 = 7.007 inches (or rounded down 7) -This is your riser height for EACH RISER

Adjust up or down as needed to meet code/preferences (ex. If you wanted a higher riser height than 7 and want to shorten the total run of your stairs, simply take 119.125 (total rise) / 16 [rounded 17.018 down to the next lowest whole number] = 7.45 riser height.

Step 5. Find the total number of treads

17 risers -1 = 16 treads

Step 6. Find the total run by multiplying the ideal tread width x # of treads

16 treads x 11 ideal tread width = 176 (14 8) total run

A few notes for residential straight treads:

Ideal Riser height is around 7 inches, Ideal Tread width is around 11 inches

Code Allowed Rise: 8 MAX Code Allowed Tread width: 9 MIN

For a nice set of stairs: 2 rise + 1 tread = 25