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Concrete Stairs Calculator

Volume from the stepped section, not from a length

Double the number of steps and you nearly quadruple the concrete. Each step stands on every step below it, so the section of a flight is a triangle rather than a strip, and the volume grows with the square of the count.

Concrete stair takeoff

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Volume from the stepped geometry. Riser and tread dimensions are governed by IRC R311.7 and this page does not check them: the stair construction calculator reads that section in full.

Specification summary

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Entered

Result

This figure is drawn from the flight you type in above.
Why a flight is not its length times a step

Worked example

A five riser flight, 7 in rise, 11 in tread, 48 in wide, poured solid in a severe weathering region.

  1. The section is not five steps, it is fifteen. Step one stands on nothing, step two on one, step five on four. So the cross-section is 1+2+3+4+5 = 15 step units of 77 square inches, which is 5 x 6 / 2.
  2. That is 1.19 cubic yards. Eight square feet of section, 48 in wide.
  3. Now build ten risers instead of five. The section goes to 10 x 11 / 2 = 55 units, and the concrete to 4.36 cu yd. Twice the steps, 3.7 times the concrete, and the same arithmetic runs the other way: halving a flight cuts far more than half.
  4. The formwork is the cost, and it does not follow the volume. Five risers is 42.4 square feet of formed and finished surface for 1.19 cu yd, which is 35.7 sq ft per yard. A flat slab is about 27. Every one of those square feet is braced, poured against and finished by hand.
  5. And in a severe weathering region the mix is specified. Table R402.2 names exterior steps explicitly, which most flatwork on this site only fits by analogy: 3,500 psi and mandatory air entrainment.

The volume is the number people ask for and the formwork area is the number that predicts the quote. Concrete stairs cost what they do because of the second one.

The formula

The section is a triangular number, which is where the square comes from:

section = R × T × n(n + 1) / 2    volume = section × W
R, T
the rise and tread of one step, which give the area of one step unit
n(n + 1) / 2
how many of those units are in the flight: 1 + 2 + ... + n
W
the stair width, the only term that scales linearly

For large n that triangular number is close to n squared over two, which is why doubling a flight roughly quadruples it. It also means the marginal step is the expensive one: going from nine risers to ten adds ten units, while the first step added one.

What this page does and does not check

It computes volume and formwork area from the geometry you give it. It does not check the geometry against the code. Riser height, tread depth, the relationship between them and the 3/8 in tolerance across a flight are all in IRC R311.7, and the stair construction calculator on this site reads that section in full.

Which matters more on concrete than on timber. A wooden stair with a riser out of tolerance can be shimmed. A poured one cannot be adjusted at all once it has gone off, and the commonest way a concrete stair fails inspection is a first or last riser that differs from the rest because the landing was not where the drawing said.

Table R402.2 names exterior steps directly, which is unusual: most of the exterior flatwork on this site fits that row only by analogy. Steps are in the text alongside porches, carport slabs and garage floors, so the strength requirement is not an inference here.

Reinforcement is not on this page. A flight of steps spanning between a footing at the bottom and a landing at the top is a structural element, and how it is reinforced depends on that span and on what is underneath. Steps poured on well compacted ground are a different problem from steps bridging a void.

Prices for ready-mix and bagged concrete

The published figures for ready-mix and bagged concrete are on the concrete calculator, with the byline, the publication date and the caveats that go with them. They are not repeated here, because the same table on two pages is worth less than one table you can find.

This site publishes no price of its own. Why, and what that means for these figures.

Solid or a shell, and what the fill has to do

Nobody pours a tall flight solid, and the calculator will work it either way because the difference is large.

A shell is the treads, the risers and the two sides, poured over compacted fill. On a five riser flight that is about a third less concrete, and on a tall flight it is far more, because the solid volume grows with the square and the shell area does not.

The fill is doing structural work, which people underestimate. It is what the treads are bearing on, so it has to be placed in lifts and compacted like a base course, not tipped in and levelled. A shell over loose fill cracks along the nosings, which is both the most visible place and the most dangerous one.

And it has to drain. Fill under a stair that holds water will heave in a freeze, and it will lift the treads unevenly, which is exactly the defect R311.7's tolerance rules exist to prevent.

If the ground under the stair is not good enough to be trusted, the answer is a spanning flight rather than a thicker shell, and that is an engineered element.

Why stairs cost more than their volume suggests

The calculator prints formwork area per cubic yard for one reason: it is the number that explains the quote.

A slab is about 27 square feet of surface per cubic yard. One face, formed at the edges only, floated flat in one pass.

A five riser flight is 35.7, and a shell over fill is nearly 50. Every riser is a formed face, every tread is a finished surface, both sides are formed full height, and all of it has to be braced against the pressure of wet concrete pushing outwards and downwards at once.

The bracing is the part that surprises people. Riser forms want to float up and bow out, and they are being loaded by concrete that is deepest exactly where the form is tallest. Stair formwork is closer to carpentry than to slab edging.

And the finishing is on a timer. Treads have to be floated and edged while the concrete is still workable, and there are as many separate surfaces as there are steps, each reachable only from one direction.

So a flight that is a cubic yard and a half of concrete can be a two day job for two people. The volume tells you what to order. The formwork area tells you what it will cost.

Frequently asked questions

How much concrete for concrete steps?
Work the section as a triangular number, not a length. A five riser flight at 7 in rise and 11 in tread is 1+2+3+4+5 = 15 step units of 77 sq in, so 1,155 sq in of section, which at 48 in wide is 1.19 cubic yards. Ten risers is 55 units and 4.36 cu yd.
Why do more steps cost so much more?
Because each step stands on every step below it, so the section is a triangle rather than a strip. The volume grows with n(n+1)/2, which for larger flights is close to the square of the riser count. Twice the steps is roughly four times the concrete, and the last step added is the most expensive one.
Should concrete steps be poured solid or as a shell?
A shell over compacted fill on anything but a short flight, because the solid volume grows with the square and the shell area does not. The fill is doing structural work: it has to be placed in lifts, compacted properly and able to drain, or the treads crack along the nosings.
What strength concrete for exterior steps?
IRC Table R402.2 names exterior steps explicitly, alongside porches, carport slabs and garage floors: 2,500 psi in a negligible weathering region, 3,000 in moderate and 3,500 in severe, with air entrainment mandatory in the last two. That is a direct requirement rather than an analogy, which is unusual for exterior flatwork.
Does this calculator check the riser height against the code?
No. Riser height, tread depth and the 3/8 in tolerance across a flight are in IRC R311.7, and the stair construction calculator on this site reads that section in full. It matters more on concrete than on timber, because a poured riser cannot be shimmed afterwards.
Why is stair formwork so expensive?
Because there is far more of it per cubic yard than on any slab. A flat slab is about 27 square feet of surface per cubic yard; a five riser flight is 35.7, and a shell over fill approaches 50. Every riser is a formed face, every tread is a hand-finished surface, and the forms have to be braced against concrete that is deepest where the form is tallest.
Do concrete steps need a footing?
They need to bear on something that will not move, and what that is depends on the ground and the frost line. Steps sitting on compacted fill over good ground are one thing; steps at the edge of an excavation or spanning to a landing are a structural element and outside this page. Frost depth is local and is not published here.

Check these numbers yourself

How every figure here is verified: Sources & Method. Who builds this: About. Found something wrong? Tell us and it gets fixed or removed.

Figures on this page last checked against the source documents on 2026-09-09. Codes are amended locally; confirm against the edition your jurisdiction enforces.

Related calculators

This computes volume and formwork, not compliance. Riser and tread dimensions are governed by IRC R311.7 and are not checked here, which matters more on concrete than on timber because a poured riser cannot be adjusted afterwards. Reinforcement, bearing and frost depth are all outside this page, and a flight spanning to a landing rather than bearing on ground is an engineered element.