Stair Stringer Calculator

How the stringer layout is calculated

Stair layout starts with total rise: the exact vertical distance from the top of the lower finished floor to the top of the upper finished floor. That number gets divided as evenly as possible into individual risers, because building codes and basic safety both require every riser in a single flight to be nearly identical — an uneven step is one of the most common causes of stair trips and falls.

This calculator divides total rise by your target riser height and rounds to the nearest whole number of steps, then divides the total rise by that whole number to get the actual riser height everyone in the stair will use. It's normal for the actual riser to come out slightly different than the target you entered, since a whole number of equal steps rarely divides your rise exactly.

Tread depth is entered directly and multiplied by one less than the number of risers (there is always one fewer tread than riser in a stair, since the top step is the landing) to get the total horizontal run the stringers will need.

Where these numbers come from

The formula and default values in this calculator are based on:

• Riser/tread proportioning method and the 2R+T comfort rule of thumb reflect long-standing stair layout practice found in residential building codes (e.g., IRC stair provisions) and standard carpentry references.

These are planning estimates. Check your local building code, product specifications, and a licensed contractor before you buy materials or build.