Concrete Steps Calculator

Concrete Steps formula

Step volume (cu ft) = Riser (in) / 12 x Tread (in) / 12 x Width (ft) x (1 + 2 + ... + number of steps)
Platform volume (cu ft) = Steps x Riser (in) / 12 x Platform depth (in) / 12 x Width (ft)
Cubic yards = (Step volume + Platform volume) x (1 + waste %) / 27
Bags = Cubic feet with waste / bag yield  (80 lb = 0.60 cu ft, 60 lb = 0.45 cu ft)

Worked example

Four steps with 7.5 in risers and 12 in treads, 5 ft wide, with a 24 in landing at the top: one riser by one tread by the width is (7.5 / 12) x (12 / 12) x 5 = 3.125 cubic feet. The four layers count 1 + 2 + 3 + 4 = 10 units, so the steps are 31.25 cubic feet. The landing is 4 x 7.5 / 12 = 2.5 ft tall, 2 ft deep and 5 ft wide, another 25 cubic feet.

Total 56.25 cubic feet. With 10% waste that is 61.9 cubic feet, or 2.29 cubic yards, which would take 104 bags of 80 lb mix. That size job is better ordered as 2.5 yards of ready-mix.

Quick reference

How to calculate concrete for steps

Think of solid steps as a stack of slabs. The top slab is one riser tall and one tread deep. The one under it is one riser tall and two treads deep, and so on down to the bottom slab, which runs the full length of the stair. Multiply riser by tread by width for the smallest slab, then multiply by 1 + 2 + 3 up to the number of steps. If the top step is a landing, add its extra depth as a block the full height of the stair.

Measure the total rise from the lower grade to the door threshold or upper slab, then divide by a riser height near 7 inches and round to a whole number of steps. All risers must be the same height within 3/8 inch, so adjust the riser rather than making the last step different.

Forming and pouring

Set the steps on a footing or a compacted gravel base and, in cold climates, take the footing below the frost line so the steps do not heave away from the house. Form the risers with 2x8 lumber beveled at the bottom edge so you can trowel the whole tread. Tie the steps to an existing slab or foundation with rebar dowels.

For stairs more than a few feet tall, fill the center with compacted gravel or clean rubble and pour only a 6 to 8 inch shell around it, which can cut the concrete by half or more. Pour from the bottom step up, rodding each riser to remove air pockets, and strip the riser forms as soon as the concrete holds its shape to finish the faces.

Key facts

• The IRC limits risers to 7.75 in and requires treads at least 10 in deep, with no more than 3/8 in variation between steps.
• Three 7 x 11 in steps 4 ft wide use about 12.8 cubic feet of concrete, roughly 22 bags of 80 lb mix before waste.
• Concrete for steps grows quickly: six steps use about 3.5 times as much as three steps of the same size.
• Two risers plus one tread should total 24 to 25 in for a comfortable stair.
• Solid steps taller than about 3 ft are often poured over a fill of compacted gravel or rubble to save concrete.

Frequently asked questions

Sources and references

• •QUIKRETE Concrete Mix No. 1101 product data sheet (Quikrete)
• •Sakrete High-Strength Concrete Mix product page (Sakrete)
• •Chapter 3 Building Planning (Section R311.7 Stairways), 2021 IRC (ICC)