Concrete Stairs Calculator
Calculate concrete volume, bags and rebar for poured concrete stairs - by step count, tread and riser dimensions.
The concrete stairs calculator returns volume, bags and rebar for poured concrete steps - front porch stoops, deck stairs, retaining wall steps or any code-compliant stair. Stair geometry follows the 2R + T = 24-25 rule of thumb: a 7 inch riser pairs with 11 inch tread, a 7.5 inch riser pairs with 10 inch tread. The calculator works out the triangular side profile (the wedge formed by the step stack), adds the top platform extension and multiplies by the stair width to get total volume. Standard reinforcement is #4 rebar - two horizontal bars at each tread level plus vertical bars every 12 inches of stair width.
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Frequently asked questions
A 5-step stair with 7 inch risers (35 inch total rise), 11 inch treads (55 inch total run), 4 ft wide and a 12 inch top platform extension needs about 13.8 cubic feet (0.51 cubic yards). That is 23 bags of 80lb concrete or 31 bags of 60lb with 10% waste. Above 1 cubic yard, ready-mix is cheaper than bagged.
7 inch riser and 11 inch tread is the IRC residential standard. The rule of thumb is 2R + T = 24-25 inches for a comfortable stair. Maximum riser is 7.75 inches by IRC code; minimum tread is 10 inches. Outdoor stairs often use 6 inch riser / 12 inch tread for a slower, more comfortable climb.
Yes for any stair over 2 steps. Standard reinforcement is two #4 (1/2 inch) horizontal bars at each tread level, plus vertical bars every 12-16 inches of stair width tied to the horizontals. Without rebar, concrete stairs crack at the tread-riser joint within a few freeze-thaw cycles. Outdoor stairs in cold climates also need a frost-protected footing under the bottom step.
Yes - always one continuous pour, never one step at a time. A monolithic pour bonds the entire stair into a single structural unit. Pouring step by step creates cold joints that fail at the tread-riser line. For large stairs (over 1 cubic yard), use ready-mix delivered for that single pour. Smaller stairs (under 0.5 cubic yards) can be hand-mixed from bags if you have enough hands to keep up.
Yes - the bottom of the stair sits on a footing below frost line, just like a deck or fence post. In northern US states this typically means 36-48 inches deep. For attached stairs (a stoop coming off a porch), the stair can be tied into the existing porch footing. Free-standing stairs always need their own footing or they will heave and crack with frost.