Concrete for a flight of steps — and the riser layout that divides your rise into equal, code-legal steps.
Concrete Steps Calculator
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Count only the treads you are casting. Stepping up onto an existing porch, that porch is not one of them.
Compacted fill inside a big stoop, cast around. Leave 0 for solid steps.
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24 × 80 lb bags
V = width × rise × run × n(n+1)/2
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Calculated with BuildCalculators.com · buildcalculators.com/concrete-steps-calculator
Estimates are for planning only — confirm quantities with your supplier or contractor before ordering.
A flight of steps is the shape people most often get wrong by hand, because the instinct is to multiply the overall box and take half. It is not half. A flight is a stack of slabs — the bottom one as deep as the whole flight, the next one tread shorter, and so on up to a single tread at the top — and summing that stack gives width × rise × run × n(n+1)/2.
The n(n+1)/2 is the part worth internalising: the concrete follows a triangular number, not a straight line. Three steps take six tread-blocks of concrete; six steps take twenty-one. Doubling the steps very nearly quadruples the pour, which is why a stoop that looked like a bag job turns into a truck as soon as the porch is a little higher.
V = width × rise × run × n(n+1)/2risers × riser heighttreads × tread depthtotal rise ÷ risers, all equalceil(total rise ÷ 7.75 in)IRC R311.7.5.1 caps the riser at 7¾ inches and allows the largest and smallest in one flight to differ by no more than ⅜ inch. That second limit is the one that dictates the method: you cannot make up a remainder on the top or bottom step. So take the total rise, divide by 7.75, round UP to a whole number of risers, then divide the rise by that count to get the exact riser height. A 30 inch rise gives four risers of 7.5 inches — not three of 7.75 plus a short one.
The surface you step up onto — the porch, the landing, the door threshold — is the last tread, and it already exists. So a flight with four risers has three concrete treads. Counting four treads is the most common way people over-order, and on a 4 ft wide flight it is an extra 8½ cubic feet.
Not from bare dirt, and not from the excavation. If paving, gravel or topsoil is going down after the steps, the total rise shrinks by exactly that depth and every riser changes with it. Steps laid out before the finished grade was established are the classic cause of a short bottom step — which is both a trip hazard and a code failure, because it makes the flight unequal.
A large stoop is often built as a shell over compacted fill rather than as a solid block, and on a big set of steps that can halve the pour. It works only if the concrete around the fill is thick enough to span — keep 4 to 6 inches over the fill on every tread and riser, reinforce it, and compact the fill in layers as it goes in. Fill that settles later takes the tread down with it, and there is no repairing that from above.
A flight of steps is a heavy, narrow load bearing on a small footprint, and it is attached to nothing. Set it on a footing below the frost line. Steps that have pulled away from a house — the gap you see at the top riser on countless porches — are almost always steps that were poured onto topsoil and then heaved.
Each tread wants about ¼ inch of fall over its depth so water runs off rather than sitting and freezing. And a stairway serving a dwelling needs 36 inches of clear width; outdoor steps are usually wider for looks, but the minimum is a minimum.
7 in risers, 11 in treads, poured solid.
0.52 yd³, or 24 bags
Half a cubic yard: comfortably a bag job, but 24 bags is nearly a ton to mix in one continuous pour. Two people minimum.
Same width, same rise and run — a higher porch.
1.66 yd³ — order a truck
This is the n(n+1)/2 effect in one comparison. Doubling the step count did not double the pour; it more than tripled it, and it crossed the line from bags to a delivery.
Ground to porch is 30 in. What are the steps?
Four risers of 7.5 in, three treads
Three risers would be 10 inches each — well over the limit. Four equal risers of 7.5 is the answer, and "equal" is not negotiable: the code allows 3/8 in of variation across the whole flight.
7 in risers, 11 in treads, 4 ft wide, poured solid, before waste.
| Treads | Total rise | Volume | Cubic yards | 80 lb bags |
|---|---|---|---|---|
| 1 | 7 in | 2.14 ft³ | 0.08 yd³ | 4 |
| 2 | 14 in | 6.42 ft³ | 0.24 yd³ | 11 |
| 3 | 21 in | 12.83 ft³ | 0.48 yd³ | 22 |
| 4 | 28 in | 21.39 ft³ | 0.79 yd³ | 36 |
| 5 | 35 in | 32.08 ft³ | 1.19 yd³ | 54 |
| 6 | 42 in | 44.92 ft³ | 1.66 yd³ | 75 |
Smallest whole number of equal risers that stays under 7¾ in.
| Total rise | Risers | Each riser | Treads | Total run at 11 in |
|---|---|---|---|---|
| 12 in | 2 | 6.00 in | 1 | 11 in |
| 18 in | 3 | 6.00 in | 2 | 22 in |
| 24 in | 4 | 6.00 in | 3 | 33 in |
| 30 in | 4 | 7.50 in | 3 | 33 in |
| 36 in | 5 | 7.20 in | 4 | 44 in |
| 45 in | 6 | 7.50 in | 5 | 55 in |
| 54 in | 7 | 7.71 in | 6 | 66 in |
IRC R311.7. Local amendments vary — check yours.
| Dimension | Limit | Section |
|---|---|---|
| Riser height | 7¾ in maximum | R311.7.5.1 |
| Tread depth | 10 in minimum | R311.7.5.2 |
| Riser variation in a flight | ⅜ in maximum | R311.7.5.1 |
| Tread variation in a flight | ⅜ in maximum | R311.7.5.2 |
| Clear width | 36 in minimum | R311.7.1 |
Poured concrete steps run $300–$900 for a small three-step stoop installed, and $1,500–$5,000 for a wide flight with landings and railings, in 2026. Materially the concrete is minor — a three-step flight is under $200 of mix — because the cost is in the formwork, which has to be built, braced, and stripped without damaging the arrises.
Every riser is a board that has to be held straight against wet concrete pushing on it, and the two side cheeks are cut to the exact stair profile. A three-step flight has enough forming in it to take a competent carpenter most of a day, which is why installed prices look so high against a $200 material bill.
On anything above about four steps, building a shell over compacted fill saves real money — both in concrete and in the reinforcement a solid block of that size would want. Below four steps the saving is small and the extra complication is not worth it.
Precast concrete steps arrive as a unit and are set in an afternoon, typically $500–$1,500 delivered and placed for a small flight. They cost more than site-pouring the concrete and less than site-forming it, and the finish is consistent. Where they lose is fit: a precast unit comes in fixed rises, and your ground-to-porch dimension is whatever it is.
It is n(n+1)/2 tread blocks, which works out at (n+1)/2n of the bounding box — 67% for three steps, 58% for six. Halving the box under-orders every time, and the shortfall grows with the flight.
The surface you step onto already exists. Four risers means three concrete treads. Counting four adds a full tread block to the order.
All risers in a flight must be equal within ⅜ inch. Dividing the rise by 7.75 and putting the leftover in the bottom step fails inspection, and it is also the step people trip on, because the body has already learned the rhythm of the others.
Paving, gravel and topsoil all raise the ground after the steps are laid out. Measure from where the ground will end up, or every riser is wrong by that depth.
Steps need a footing below the frost line like anything else. The gap you see between a porch and its steps on so many houses is the result of skipping it.
About ¼ inch of fall across the tread sheds water. Level treads hold puddles, and in a freezing climate that is a sheet of ice on the one surface you cannot avoid walking on.
Volume = width × rise × run × n(n+1)/2. A 4 ft wide flight of three treads at 7 inch rise and 11 inch tread is 12.83 cubic feet, or 0.48 cubic yards — about 24 bags of 80 lb once waste is added.
Because a flight is a stack of slabs of different depths: the bottom one spans the whole flight, the next is one tread shorter, and so on. Summing them gives a triangular number. The practical consequence is that doubling the steps more than triples the concrete — three treads take 6 tread blocks, six take 21.
Four risers of exactly 7.5 inches. Divide 30 by the 7¾ inch maximum, round up to 4, then divide 30 by 4. Three risers would be 10 inches each, well over the limit.
7¾ inches under IRC R311.7.5.1, with a minimum tread depth of 10 inches. The largest and smallest riser in one flight may differ by no more than ⅜ inch, which is why you cannot leave a remainder on the bottom step.
Yes. Steps are a heavy narrow load on a small footprint, attached to nothing. The footing goes below the frost line. The gap you see between a porch and its steps on so many houses is the result of pouring onto topsoil instead.
On a large stoop, yes, and it can halve the pour. Keep 4 to 6 inches of reinforced concrete over the fill on every tread and riser, and compact the fill in layers as it goes in. Fill that settles later takes the tread down with it.
36 inches is the code minimum clear width for a stairway serving a dwelling. Most front steps are built wider — 4 to 5 feet — because a narrow flight looks mean against a house, and the extra concrete is a small share of the job.
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