How to Figure out the Rise & Tread for a Staircase

Local building codes list allowed measurements for rises and treads.

Local building codes cover the design and construction of staircases, including rise and tread measurements. The rise is the vertical distance between the front edge of two treads. The tread is the part of the stair where you place your foot. Uniform measurements allows users to maintain their gait and balance on the staircase. Many local governments use the International Residential Code, which is a model and uniform building codes, while other jurisdictions develop their own codes. After determining the appropriate code for the staircase, whether interior or exterior, a standard calculation method is used.

Things You'll Need

• Measuring tape
• Calculator

Instructions

1. Measure the total rise, which is the vertical distance of the space for the staircase from floor to floor or from the starting point that will be the bottom of the staircase to the top of the landing. A sample measurement for the total rise is 8 feet 10 ¾ inches.

2. Convert the measurement into inches only. The total rise height of 8 feet 10 ¾ inches converts to 106 3/4 inches (or 106.75 inches).

3. Divide 106.75 by 7.5, which is considered an ideal rise height, to determine how many steps you will need in your staircase. For instance, 7.5 divided into 106.75 equals 14.233. Drop the .233 since a partial step is inappropriate and continue with 14 equal increments or steps.

4. Divide the total rise by 14, as in 106.75 divided by 14 equals 7 5/8 or 7.625. Drop one step to perform the calculations for the treads. The top of the landing is the final step, which requires omitting the 14th rise.

5. Measure the run, which is the distance from the wall that supports the upper landing extending out to the point at which the staircase begins. For instance, a run of 11 feet, 2 7/8 inches converts to 134.875 inches.

6. Divide 134.875 inches by 13 steps, which results in 10 3/8 inches or 10.375 inches for each stair tread.

Tips & Warnings

• Building codes usually list the minimum and maximum allowed tread widths and the formulas to determine the proper tread-to-rise ratios.

• The 2006 International Residential Code lists a minimum of 36 inches wide for a staircase. The width of treads will be slightly less than the allowed staircase width.

• The final run measurement for each step will be higher because of the riser below the bottom step and the bull nose of the tread. The bull nose is the molding applied to the front and edges of the treads.

• Other measurements, such as headroom, might affect the calculations for risers and treads.

• Use an online calculator to figure the measurements for rises and treads. You can also purchase a handheld calculator that determines the measurements.

References

• Stairway Manufacturers’ Association: The Staircase
• Stairway Manufacturers’ Association: Glossary
• Carpentry Pro-Framer: Stairs
• Arcways: Visual Interpretation of the International Code 2006 Building Stair Building Code

Resources

• Stairway Manufacturers’ Association: SMA Visual Interpretation of the Stair Building Code 2009 International Residential Code
• EZ Stairs.com: Stair Calculator