Stair calculator
For a 100-inch total rise, you need 13 risers. The count comes from dividing the total rise by the 7.75-inch riser cap: 100 / 7.75 = 12.9, which rounds up to 13 so no single step exceeds the code maximum. That is the number of steps your stairway has.
Stairs
You can set the tread run higher than the 10 in residential minimum.
Tap or type into any yellow number on the drawing to change it.
Building code caps riser height at 7.75 inches, the tallest a single step may be. Divide total rise by that cap and round up to get the riser count. Each riser then equals total rise divided by the count, so all steps are equal. Treads are one fewer than risers because the top floor is the final surface. Tread run must be at least 10 inches. Stringers, the diagonal boards that run top to bottom and have the steps cut into or attached to them, are planned around a nominal 16-inch on-center spacing; a 36-inch-wide stair takes 3 stringers, which puts them 18 inches apart. Turning staircases come in L-shaped, U-shaped, and landing versions on this site.
The calculator switches total rise, tread run, and width between inches and centimeters based on the unit system you choose.
What is the reason the riser count is rounded up rather than down?
Rounded up ensures no riser exceeds the 7.75-inch code cap. If you rounded down, at least one riser would be taller than allowed, and steps would be uneven. Rounding up gives a whole number of equal-height risers that all fit under the limit.
How do a riser and a tread differ?
The vertical part of a step, including its height, is the riser. A tread is the flat part you put your foot on. The final surface, whether the top landing or the floor, accounts for the missing tread, so the tread count is one less than the riser count.
How many stringers does a stairway need?
Divide the stair width by 16 inches, round down to a whole number, then add one for the starting stringer. The count therefore depends on the width. The resulting spacing is typically about 16 inches on center but can be wider; a 36-inch-wide stair takes 3 stringers, which puts them 18 inches apart.