Use this automatic stair calculator for applications requiring the risers to be 7 3/4″ maximum. Use the number boxes to enter a value for the vertical rise. The results returned are the number of steps along with the risers and the angle of the stringer. Includes a landing section for finding the individual step height from the top down or from the bottom up. Also determines the required length of lumber to make the stringer. See instructions below.
How to Calculate Step Risers
- Take a direct measurement from the top of the finished floor at the bottom to the top of the finished floor at the top. Since the finished flooring is not installed, use small pieces to simulate it.
- Use the number boxes to enter a value for the vertical rise in feet, inches, and fraction, or inches and fraction. The results returned are the number of steps and the individual riser.
- If there is a landing, then use the “Top of Which Step” to enter a step number from the top down or from the bottom up. Remember, this value is for the finished floor. Make adjustments accordingly when laying out the marks for the landings. For example, if the landing is finished with 3/4″ hardwood then build the rough framing 3/4″ lower to compensate for the added height when the landing is finished.
- The required length of board for the stringer is an approximation. This takes into account for a 10″ run and assumes the top step will be the floor.
Laying out a Stringer
Once the number of steps and the risers has been determined, prepare a good quality piece of lumber on a set of sawhorses for lay out.
- Turn the crown towards you.
- Start on the right hand side and make that the top.
- The number of steps returned by the calculator can be reduced by one if the stringers drop down one step at the top.
- Use a framing square. Place the tongue on the calculated riser and the blade on 10″ (or the selected run). Be sure you are certain of the finished tread heights and make any adjustments necessary.
- For example, on the bottom step when hardwood is on the beginning floor and one inch thick treads are used for steps, then it boils down to removing 1/4″ from the bottom of the stringer.
Staircase Terms and 2012 IRC Building Codes
These building code requirements are based on information beginning on page 89 of the 2012 International Residential Code.
A staircase (set of steps) must not exceed 12′ between landings or floors. They must provide safe passage from one floor to the next.
The vertical rise of the steps is the distance from the top of the finished floor on the beginning level to the top of the finished floor on the ending level. At no point can this exceed twelve feet.
The risers are the result of dividing the total rise by the number of steps it takes to be as close to 7 3/4″ as possible without going over. They must be within 3/16″ of each other on all steps.
At no point can the head room drop below 6′ 8″. This is measured vertically from a straight edge along the leading edge of the steps up to the lowest point in the ceiling.
The width of the stairway can not drop below 36″. Handrails can not interfere with this by more than 4 1/2″ each. Minimum distance between two handrails can not drop below 27″.
Treads can be no less than 10″ wide. Remember that temporary treads are just temporary. Do not forget this when laying out the stringer.
There must be a landing at the top of a flight of stairs if a door swings out over it. The landing must have a minimum width of 36″, but if the door is larger, then it must match its size.
The run for each step must be no less than 10″ as long as there is a one inch overhang on each tread. If there is no overhang, then the run must be 11″.
For details on winder stairs click here.
For details on handrails click here.
Do I count my steps to the landing from top down or from the bottom up?
It depends on the situation. Most of the times it is better to count the steps and measure them from the bottom up simply because you have something to start with (the floor). Other situations demand that you count from the top down. This is specifically true when trying to cut in a set of steps with multiple landings and the top is fixed., or if the bottom is not clearly defined as can be on outdoor projects. If you can not move the last step, then you might as well start there and work down.
Sawing a Stair Stringer
Safety first when using any power tools. Always wear safety glasses. Use two hands on the saw at all times. If the blade begins to bind, even though it my be following the mark, then back it up and come again as many times as necessary.
Use a quality 7 1/4″ circular saw with a god sharp framing blade to cut the pattern. Make sure to keep the marks between your eyes and the blade and to keep the blade on the side of the line that maintains the stringers dimensions. This will involve watching the blade of the saw from one side to the other. It takes a little getting used to, but its worth it. This is a skill that separates the men from the boys. Keep your eyes on the saw blade and know which side to watch it from.
Be careful with the back cuts (the distance the saw must travel past the intersection of the marks to complete the cut). Be sure the table is all of the way down and the back cut can be around an inch. Some people accept none whatsoever. In this case the cuts must be finished with another saw such as a handsaw or jig saw.
Once the pattern for the stair stringer has been established, it should be used to duplicate its shape onto the other boards that will be used for the stair stringers. Be careful when marking other stringers from a pattern. It makes no difference if it was created with a calculator if you not going to mark the duplicates accurately.