Concrete stairs calculator
This estimates the stepped wedge from the sizes you enter and rounds a shade high on purpose. It does not design the stair, its reinforcement or the slab that carries it, and it is not the building code's riser and tread limits. Pour to your drawings and check the order with your supplier.
Enter the step count, the riser and tread and the width, and the tool estimates the concrete in the stepped mass — a triangular wedge whose height is the total rise and whose base is the total run — then converts it to yards, metres and bags.
Worked example
Five steps at a 7-inch riser and an 11-inch tread give a total rise of 35 in (2.92 ft) and a total run of 55 in (4.58 ft). The wedge cross-section is ½ × 2.92 × 4.58 ≈ 6.69 ft²; at 3 ft wide that is 20.1 cubic feet, or 20.1 ÷ 27 ≈ 0.74 yd³. Add 10% and you would order about 0.82 yd³.
The formula
volume ≈ ½ × (steps × riser) × (steps × tread) × width
Total rise is the step count times the riser; total run is the step count times the tread. Half their product is the area of the triangular side of the wedge, and multiplying by the width sweeps that triangle across the stair. Feet cubed divide by 27 for yards; metric comes out in cubic metres directly.
What this tool assumes
That the poured mass is a triangular wedge — a fair, faintly generous stand-in for the true stepped shape. Riser, tread, width, waste and bag yield are all fields you set. The only baked figure is the 27-cubic-feet-per-yard definition.
Questions
- How do I calculate concrete for stairs?
- The solid mass under a run of steps is close to a triangular wedge: half of the total rise times the total run, times the stair width. A flight of 5 steps at a 7-inch riser and an 11-inch tread, 3 feet wide, works out to roughly 3.7 cubic feet of the wedge — enter your own figures above and the yardage and bag count appear instantly.
- Is the wedge estimate exact?
- It is deliberately a slight over-estimate, and that is the useful direction to err. Poured steps sit as a stack of boxes on top of a sloping slab; the true shape is the triangle plus the little square nose of each step. The half-rise-times-run wedge captures the bulk and rounds your order up, which beats running short mid-pour.
- What if the stairs sit on a supporting slab or wall?
- Then work that part out separately. This tool covers the stepped wedge itself. A throat slab beneath it, a landing at the top, or side cheeks are each their own rectangular pour — the slab and footing tools handle those, and you add the volumes together.
- How many bags will a short flight take?
- The bag count sits beside the volume, using a yield you can edit. Small exterior flights are firmly bag territory — a few steps rarely justify a truck and its minimum charge. Once the flight is wide, tall, or one of several, price a ready-mix delivery against the bag tally the tool gives you.
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