Solid concrete steps are a durable entrance to a porch, a deck or a garden terrace. Before building the forms, you need to know how much concrete to order. This calculator adds up the volume of the stepped block and a top landing.
How the volume is calculated
Solid steps form a staircase-shaped block. Each step adds a slab one tread deep, at the height of all the steps below it plus its own:
steps volume = width × run × rise × n × (n + 1) ÷ 2
The landing at the top is a block as deep as you choose and as high as all the steps:
landing volume = width × landing depth × n × rise
The calculator adds a margin for spillage, uneven ground and form bulging, 10% by default.
Example
Three steps, 48 in wide, with a 7 in rise and 11 in run, and a 36 in landing:
- steps: 48 × 11 × 7 × 6 = 22,176 in³;
- landing: 48 × 36 × 21 = 36,288 in³;
- total: 58,464 in³ = 33.8 ft³, or 37.2 ft³ with 10% extra;
- that is 1.38 cubic yards, or 63 bags of 80 lb premix (0.6 ft³ each).
Above about 1 cubic yard, ready-mix delivered by truck is usually cheaper and much easier than mixing 60 bags by hand.
Step dimensions
- Rise: 6 to 7.75 in. The International Residential Code limits stair risers to 7.75 in.
- Run: at least 10 in, and 11 to 12 in feels more comfortable outdoors.
- Consistency: all risers should be equal within 3/8 in, as should all treads, so nobody trips.
- Slope: give each tread about 1/8 in per foot of slope toward the front so water drains off.
- A landing at least 36 in deep is common in front of a door; local codes may require one.
Saving concrete
For tall or wide steps, fill the core with compacted gravel, rubble or a cardboard void form, keeping at least 4 in of concrete everywhere. The calculator assumes fully solid steps, so it gives the maximum.
Building tips
Steps must rest on a proper footing below the frost line in cold climates, or on a compacted gravel base, and be tied to the foundation if the code requires it. Use rebar for strength, bevel the form boards at the bottom of each riser so you can finish the tread, and keep the concrete moist for several days while it cures.