Concrete Step Calculator

Stairs are stacked slabs

The easiest way to picture a set of steps is as layers. The bottom layer runs the full depth, from the front of the first step to the back of the landing. Each layer above is one tread shorter.

In the worked example, 3 steps with a 7 in rise, an 11 in tread and a 36 in landing stack as layers 58, 47 and 36 in deep. At 4 ft wide that is 1.12 cu yd with waste, or 51 bags of 80 lb.

Rise and tread come first

Measure the total height from the ground or walk to the top of the landing, then split it into equal risers. The common U.S. residential code limits risers to 7 3/4 in and requires treads of at least 10 in.

The stair calculator splits a total height into even steps. The local building code and a licensed professional have the final word on steps, landings and railings.

The landing is most of the concrete

On short stairs the top landing often holds more concrete than the steps. A deeper landing grows the bottom layer of every step below it. If the door swings out, the landing has to be deep enough to stand on while it opens.

Measure the landing depth from the house wall to the front of the top step, not to the edge of the door.

Forms and fill

Steps need side forms cut to the step profile and a riser board for each step. Bevel the bottom of each riser board so you can finish the tread under it.

Some builders put clean fill or rubble in the core of tall steps to save concrete. The calculator assumes solid concrete, so if you use fill, lower the total yourself and keep the result a little high.

Easy mistakes

• Leaving out the landing or entering it as zero.
• Using the width of the door instead of the width of the steps.
• Forgetting a footing under the steps where code calls for one.
• Ordering bags without counting the weight: 51 bags of 80 lb is over two tons.