Concrete stairs calculator

Enter the flight and this gives you the concrete for a solid pour, plus the shell-and-fill version if you are casting over compacted hardcore. The step geometry is checked against the IRC riser and tread limits as you type.

Stair width The finished width of the steps. 3 ft is a minimum for a back door, 4 to 5 ft reads as a front entrance. Number of steps (risers) Count the risers, including the last one up onto the landing or threshold. Four risers of 7 in gets you 28 in off the ground. Two is the minimum this page can answer — see below for why a single step is a different job. Riser height IRC R311.7.5.1 caps this at 7-3/4 in, and every riser in the flight has to be within 3/8 in of every other. Tread depth (run) IRC R311.7.5.2 sets a 10 in minimum. On outdoor concrete steps 11 to 12 in is worth the extra concrete — it is the difference between comfortable and careful. Top platform depth A landing in front of the door, beyond the top tread. Set to 0 if the top step lands straight onto the threshold. This is solid concrete all the way down, so it adds up fast. Shell thickness (if casting over fill) Used only for the shell and fill outputs. 5 to 6 in of concrete over compacted hardcore is the normal way to build anything more than three steps. Extra for waste % 10%. Stair formwork bulges and the treads always take a little more than the drawing says. Bag size (if mixing by hand) Steps are one of the few concrete jobs that genuinely sit on the bag side of the line.

Concrete to order, solid pour 0.52 cu yd

Same volume in cubic feet 14.1 cu ft

Bags of mix, solid pour 24 bags Rounded up, waste included.

Concrete if cast as a shell over fill 11.2 cu ft Waste included. The saving grows with the flight — small on four risers, close to half by eight.

Compacted fill under that shell 2.7 cu ft Hardcore or crusher run, compacted in layers before you form the steps.

Finished weight, solid pour 1,925 lb

Total rise 28 in

Total run 33 in

A flight of steps is not a box — but it is exactly a wedge

This is the one calculation where the shape you assume matters more than the dimensions you measure. Start with the count that catches everyone: a flight of n risers has n − 1 treads. The last riser lands you on the platform, so there is no tread above it. Four risers, three treads.

Seen from the side the flight is then n − 1 stepped rectangles, the first one riser tall, the second two risers tall, and so on:

Volume = width × tread × riser × n(n − 1) ÷ 2

Four risers 4 ft wide, 7 in high and 11 in deep is 12.8 cubic feet of finished concrete. Add a 10% allowance and you are buying 14.1 cu ft — 0.52 cubic yards, or 24 × 80 lb bags.

Two things follow, and both are exact rather than approximate:

A single box of the total rise by the total run — 28 in by 33 in here — gives 25.7 cu ft, which is exactly twice the real volume. Not roughly twice: the factor is 2 at any number of steps, because the box is the stepped solid plus its own mirror image. If a calculator hands you double what this one does, that is what it did.
A triangular wedge is not the second error you would expect. Half the box is 12.8 cu ft — exactly right. The corners the diagonal slices off each step are the same corners it adds back on the step below. Use the wedge if you like; it is the same number.

The error that does bite is counting n treads instead of n − 1. The profile then sums to n(n + 1) ÷ 2 instead of n(n − 1) ÷ 2, so the pour is inflated by (n + 1) ÷ (n − 1) — 67% on a four-riser flight, 21.4 cu ft where 12.8 is right. It gets worse the shorter the flight, and it is the error this page itself shipped with until it was checked.

Solid, or a shell over compacted fill

Steps of any size are commonly built as a 5 to 6 in concrete shell over compacted hardcore, and the outputs above give you both. On the default flight that is 11.2 cu ft of concrete against 14.1 for the solid pour, with only 2.7 cu ft of fill underneath — about a 21% saving, which is barely worth the extra work.

The reason to look at it is that the saving grows fast with the flight. A short run is nearly all shell; there is hardly any inside to fill. Take the same steps to eight risers and the solid pour is 59.9 cu ft against a 22.2 cu ft shell — now 63% of it is crusher run, and forming a shell is the obvious call.

The fill has to be compacted in layers, not tipped in. Any settlement under a step shows up as a cracked nosing, and the nosing is the part that gets stood on.

The code numbers, and the trap in the bottom step

Two limits from the IRC govern the shape:

R311.7.5.1 — maximum riser height 7-3/4 in.
R311.7.5.2 — minimum tread depth 10 in.

Both also require uniformity: the greatest riser (or tread) in a flight must not exceed the smallest by more than 3/8 in. Concrete is unforgiving here because you cannot plane a step down afterwards.

The trap is the bottom riser. Divide the total height by the number of risers and you get a clean number — then someone lays 2 in of paving at the foot of the steps, and the bottom riser is now 2 in shorter than every other one. That is a 5 in riser against a 7 in one, five times the allowed variation, and it is a genuine trip hazard as well as a failed inspection. Set your riser height from the finished ground level, not the dug level.

One step is not a flight, and this page will not size it

A flight of n risers has n − 1 treads, so at n = 1 the formula has nothing to work on and returns zero. That is not a bug to route around: a single riser with no tread above it is a threshold or a kerb, poured as a slab with a formed nose, and its volume is length × width × height rather than a stack of steps. Use the slab calculator for it and add the nose by hand.

The same limit at the other end: the platform depth field covers a landing at the top, not an intermediate landing part-way up. A flight broken by a landing is two flights — run this twice and add them.

What this does not decide for you

How the steps are supported. Concrete steps at an entrance are heavy — the default flight above weighs nearly 2,000 lb — and if they settle away from the house you get a gap at the threshold; if they are tied rigidly to a foundation that moves differently, something cracks. Whether your steps need a footing below the frost line, a keyed connection to the foundation wall, or reinforcement through the nosings is a local code and engineering question. Get the geometry and the volume here, then get the support detail from your building department.

The flight this formula assumes

n(n − 1) ÷ 2 is exact — for one particular staircase. It is a rectangular flight of identical steps, and it is the flight you should check yours against before you use the number:

One riser height and one tread depth for the whole flight. That is what the code wants anyway, but it rules out the shapes people actually build at the bottom of a flight: a flared or bullnosed first step, a wider landing step, or curved steps radiating from a door. Each of those is its own volume, added by hand.
Nothing overhangs. An overhanging nosing, a formed lip, or a chamfer on the front edge changes the concrete slightly and the formwork a lot. None of it is here.
The steps have no sides. Cheek walls, formed returns and the wing walls that flank an entrance flight are separate pours and can easily match the steps themselves in volume.
The shell figure is an estimate, not a formwork take-off. It is the length along the nosings × thickness × width, clamped so it can never exceed the solid pour. Real shell construction has a thicker slab under the bottom step and a return down each open side, both of which push the concrete back up towards the solid number. Set the shell thickness to zero and the pair reads no concrete against the whole flight as fill — that is the arithmetic's limit case, not a way to build steps.
The weight is normal-weight concrete at 150 lb per cubic foot. That is what the figure quoted above rests on. A lightweight mix weighs less, so treat that output as belonging to the mix this page assumes rather than to the one on the ticket.
The landing is solid to the ground. Platform depth is priced as full-height concrete for its whole area. If you intend to fill under the landing too, the solid output is high for you.

The steps also have to sit on something. What is under the bottom step — its footing, or the slab it lands on — is not in any of these figures.

Questions people ask

How much concrete do I need for 4 concrete steps?

About 12.8 cubic feet poured solid, for a 4 ft wide flight with 7 in risers and 11 in treads — four risers means three treads. With 10% waste that is 14.1 cubic feet, 0.52 cubic yards, or 24 × 80 lb bags, and the finished steps weigh about 1,925 lb. Cast as a 6 in shell over compacted fill instead and the concrete comes down to roughly 11.2 cubic feet with 2.7 of hardcore underneath — on a flight this short the shell saves little, because four risers is nearly all shell.

Why is this answer lower than a box calculation?

Because a box of the total rise by the total run counts the empty air above every step, and this page does not. That box is exactly twice the real volume, at any number of steps. A flight is a stack of steps: width × tread × riser × n(n−1)/2, where n is the riser count — a four-riser flight has three treads, not four.

What are the maximum riser and minimum tread for concrete steps?

IRC R311.7.5.1 caps the riser at 7-3/4 in and R311.7.5.2 sets a 10 in minimum tread, with no more than 3/8 in variation between the largest and smallest in a flight. On outdoor steps a 6-1/2 to 7 in riser with an 11 to 12 in tread walks much better than the code minimum.

Should I fill under concrete steps or pour them solid?

Fill, once the flight is tall enough for it to pay. The saving is not fixed: a 6 in shell over compacted crusher run barely beats a solid pour at four risers, because a short flight is mostly shell anyway, but the gap widens fast as the steps stack up. Change the riser count above and watch the two figures separate. Either way the fill has to be compacted in layers, or the shell cracks.

Do concrete steps need rebar?

Steps at an entrance carry real load and are exposed to freeze-thaw, so reinforcement through the nosings and dowels into the foundation are common details — but how much and where is a local code and engineering call, not something a volume calculator should decide. Ask your building department what they want to see before you form up.

Last reviewed 2026-07-31