Steps are made up of the tread, which is the part you step on, and the rise, which is the part you trip on! It’s important to have the right ratio of tread to rise to make going up and down safe and easy. In general, the smaller the rise, the bigger the tread. You should choose what’s comfortable for you but usually outdoor steps have a rise of 5 1/2 to 7 inches and a tread of 12 to 18 inches.
Once you find a ratio you think will be comfortable for you, plug it in and tweak it until it fits this formula:
Tread + (2 x rise) = 26
For example: 18 + (2 x 4) = 26
Or use this handy chart with the ratios already figured for you: