TradesHow this works
Seen from the side, a solid set of steps is a stack of rectangles: the bottom step is one riser tall, the next two risers, and so on. Add them up and the cross-section is the riser times the tread times the step count times the next number over two, and the volume is that times the width. An optional base slab under the run gets added on top.
Because each step is taller than the last, the concrete climbs with the square of the step count, so steps use more than they look. The tool gives the volume in cubic yards and the bag count in every size, and flags when the pour is big enough that ready-mix beats bagging it. It is a solid-pour upper bound, so subtract if you are forming hollow over fill.
Common questions
How much concrete for steps?
A solid set of steps is a staircase of stacked rectangles: each step is one tread deep and stands a riser taller than the one below. The volume is the width times the riser times the tread times the step count times the next number, over two. Four steps at 7 inch risers and 11 inch treads, 48 inches wide, is roughly 0.5 cubic yards with a base slab and waste.
Why do steps use so much concrete?
Because each step is taller than the last, the volume grows with the square of the step count, not in a straight line. Doubling the number of steps more than doubles the concrete. That is why a short flight of stairs can quietly cross from a bag job into ready-mix territory, and the tool flags when it does.
Does this assume a solid pour?
Yes, so it is the upper bound. Many step pours are formed hollow or poured over compacted fill to save concrete, which uses less than a solid block. If you are filling behind the risers, treat this number as the most you would need and subtract for the fill.
Sources: Solid-staircase geometry (evergreen): volume = width x rise x run x N(N+1)/2 · Bag yields: standard concrete-mix published values. Engine version 1.0.0. Risk tier 1.