Concrete Steps Calculator

A flight of solid concrete steps is really a stack of rectangular prisms. The top step is one tread deep and one rise tall; the next one down carries the tread above it plus its own rise, and so on to the bottom step, which is the tallest. Add those prisms up and the run of steps follows the arithmetic-series pattern: total volume equals width × run × rise × N(N+1)/2, where N is the number of steps. That is the same "sum of step prisms" method published concrete-step calculators use.

Because the formula works in cubic feet while you enter rise and run in inches, the calculator converts each dimension first, multiplies through, then adds a waste allowance for the forms, the sloped subgrade under the bottom step, and ordinary spillage. It divides that padded volume by each bag's yield — about 0.60 cubic feet for an 80 lb bag and 0.45 for a 60 lb bag — and rounds up, since a partial bag does you no good on the jobsite.

The tool also reports the total rise and total run of the flight so you can check the stairs against code before you build the forms: total rise is the number of steps times the rise, and total run is the number of steps times the tread depth.