Concrete for steps and stoops

How to measure

Start with the total height from the ground (or the walk) to the door threshold or deck. Divide that by about 7 inches to get the number of steps, and round to a whole number. Then divide the height by that number for the exact rise. A 21 inch climb works out to three steps of 7 inches.

The tread is how deep each step is, front to back. Ten to 12 inches is typical, and many codes ask for at least 10 inches of tread and no more than about 7.75 inches of rise. Width is the side to side size of the steps in feet. If the top step is a landing outside a door, enter its depth. A landing outside a door is commonly at least 36 inches deep. Check your local code.

The formula

This calculator treats the steps as solid concrete, poured on the ground and filled all the way down. Picture each step as its own block. The bottom block is one rise tall, the next is two rises tall, and so on. Adding them up gives:

• Volume = width x rise x tread x (steps x (steps + 1) / 2), all in feet
• With a landing, the top step uses the landing depth instead of the tread

Three steps that are 4 feet wide with a 7 inch rise and an 11 inch tread hold about 12.8 cubic feet, just under half a yard. That is about 22 bags of 80 lb mix before waste, which is why small stoops are often a bag job.

Waste factor

Step forms are built from boards, so the shape is fairly exact, but concrete still spills and forms bow a little. Ten percent is a safe default. If you fill the middle of tall steps with clean rubble or gravel, the real number will be lower than this estimate.

Tips

• Keep every rise the same height. Uneven steps trip people.
• Slope each tread slightly forward, about 1/8 inch per foot, so water runs off.
• Steps against a house often need a footing or a tie to the foundation. Ask your building department.
• Need a slab at the bottom? Use the slab calculator, and the thickness chart for how thick to pour it.