Calculating Rise and Run
Total rise is the vertical distance from the top landing to the bottom landing. Step rise is the height of each individual step, or riser.
Calculate the number of steps. Most steps have a rise between 6 and 8 inches. 8 inches is fairly high for many people and 6 may seem short, although shorter is better than higher. Begin by dividing the total rise by 7 inches and round the number up to give the number of steps. Example for a total rise of 45 inches: 45 / 7 = 6.43, rounded up = 7. So we will have seven steps.
Next calculate the step rise. Step rise = Total rise / Number of Steps. In our example, this is 45 / 7 = 6.43. So each step will rise 6.43 inches. If that seems low, try only six steps. 45 / 6 = 7.5 inches which is a more reasonable riser height.
Framing Step Forms
Build sturdy forms with 2 x 8 lumber that is ripped to the correct riser height. In our example case, we've decided on six steps, each with a riser height of 7.5 inches, so we will rip our 2 x 8 lumber to a width of 7.5 inches.
The forms are rectangular frames with the inner side open, each form built on top of the previous step. The illustration makes this clear. Use 2 x 4 stakes to hold the forms in place and 3-inch wood screws or double-headed nails for construction. Double-headed nails or screws will make disassembling the forms easy without damaging the fresh concrete.
Add braces to the front of the forms so they won't bulge, as concrete is quite heavy. For each successive step form, brace it with cross pieces nailed or screwed to the step form underneath it.
When building a stoop, add sand as fill to the inside of the forms, but don't overfill. The concrete should be at least four to six inches thick on the sides, the back and between the steps and the fill. Most contractors simply add a mound of sand inside the completed forms, or build the forms around it.
Use a spray can of vegetable oil to lightly coat the inside of the forms before pouring the concrete. This will make form removal easy and quick, while preventing damage to the fresh concrete.
If the steps you are building are against a house, you may need to attach them to the house with rebar. Always check your local building department for code information, permits if necessary, and information on local guidelines before beginning any construction project.