Steps:
1: Familiarize yourself with some basic terminology. The vertical section of a step is referred to as the "riser," and the horizontal section is called the "tread." The "stringer" runs the length of the stairs and provides support.
2:Use the measuring tape to calculate the distance from the bottom of the first floor to the top of the second floor. Note that this measurement should be made to the top of the second floor, not to the bottom of it.
3.Use a calculator to calculate the stair riser length or the number of steps you'll need.
Divide the height from the first floor to the top of the second floor by a predetermined height of your choice for the riser. The typical height of a riser is 6 or 7 inches (15 to 17.5 cm). The answer you get will indicate the number of stairs you need.
Round your calculation up or down if dividing the height to the second floor by your preferred height for the riser does not give you a whole number. For example, if the answer you obtained in the first problem was 8.5, divide your total height from top to bottom by 8 and 9 in turn. The answers from these problems will give you the riser heights for each scenario, 8 steps and 9 steps. Choose which height sounds better to you.
4.Decide on a length for the treads (the horizontal sections of your steps). You do not need to make any measurements for this, but you also do not need to choose a number at random. The typical length for a tread is 10 inches (25 cm), so you'll want to stay around that number.
5.Take the number of risers you have determined you'll need and subtract it by 1 (if you have found that you'll need 20 risers, for example, decrease that number to 19). Calculate the total length of your stairs (as opposed to height) by multiplying this number of risers (minus 1) by the length of a single tread. If you're using 10 inch (25 cm) treads and need 20 risers, you'll multiply 10 inches (25 cm) by 19 to get 190 inches (19 times 25 cm equals 475 cm or 4.75 m). This is the total length of the stairs.
6.Subtract the riser height from the total height from first floor to second floor.This answer will tell you the location of the first tread. Find the location of the second tread by subtracting the riser height from the distance from the first floor to the first tread. Continue this to find and mark on a diagram the location of and distance between all treads.
7.Measure from the bottom of where the first tread will be placed, keeping in mind that the tread will be 1 inch (2.5 cm) thick, to the top of the first riser. This is the length you need to use when cutting horizontal sections into your stringers, the two pieces of lumber that run the length of each side of the stairs to provide support.
8.Measure for a 1 inch (2.5 cm) overhang on the tread. If you're using a 10 inch (25 cm) tread, cut it at 11 inches (27.5 cm) instead so that you have some of the tread hanging over the riser.
