Calculator
Concrete Steps Calculator
Concrete steps are the trickiest of the three concrete calculators on this site, because each step isn't a simple rectangular volume — it's a stacked series of blocks, and the top step has less concrete under it than the bottom step once you account for the stair's rise. Getting this volume right matters more than on a slab, since a stair pour is usually a single continuous placement and running short mid-pour on a stepped form is a much bigger problem than on a flat slab.
This calculator sums each step's individual volume (width x depth x cumulative height to that step) rather than treating the whole staircase as one flat-topped block, which would overstate the true concrete needed.
Calculate your quantity
Concrete volume
9.63 cu ft
- Cubic yards
- 0.36 cu yd
- 80lb bags
- 17 bags
- 60lb bags
- 22 bags
- 90lb bags
- 15 bags
Shopping summary
- • 17 x 80lb bags for 3 step(s)
This is an estimate — confirm structural work with a professional.
How this calculation works
For a staircase of n steps, each step's volume = step width x step run (depth) x the height of concrete beneath that step, where the bottom step carries the full stack height and each step above it carries progressively less, since the steps above are set back and up. Sum all n step volumes, plus the volume of the footing/pad beneath the whole stair if one is being poured integrally.
This is functionally like a series of stacked rectangular slabs of decreasing height, not one solid frustum, since the horizontal footprint at each step level is a full step (not tapering) — the taper is in the vertical stacking, not the plan shape. Convert total volume to bags using the same real yield figures as the slab calculator (0.45 cu ft/60lb, 0.6 cu ft/80lb).
The formula
cuft = stepWidth × (riseIn/12) × (runIn/12) × ( stepCount × (stepCount+1) / 2 )
- stepWidth × (riseIn/12) × (runIn/12)
- The volume of ONE step-height slab across the full width and run, in cubic feet — this is the unit the whole staircase is built from, computed once and then scaled by the triangular sum below rather than recomputed per step.
- stepCount × (stepCount+1) / 2
- The triangular-number sum 1+2+...+n, standing in for the fact that the bottom step carries the full stack height while the top step carries only one riser's worth — this factor is what makes total volume grow FASTER than step count as a flight gets taller.
- no separate footing term
- This formula totals the stepped volume only — a footing or pad the staircase sits on is a genuinely separate pour with its own thickness and footprint, and has to be added by running the slab calculator alongside this one, not read off this total.
Where these numbers come from
- stacked-slab model, not a solid frustum
- The function's own code comment states the model directly: each step's plan footprint is a full rectangle (width × run), not a tapering shape, so the volume savings against a solid flat-topped block come entirely from the vertical stacking, not from any narrowing of the steps themselves.
- 7 in rise / 11 in run defaults
- Trade convention for a comfortable exterior step within most residential code ranges; entering a rise or run outside the roughly 4-8 in / 9-14 in field limits will compute a volume, but the result may no longer describe a step anyone should walk on.
- 60 / 80 / 90 lb bag yields shared with the slab calculator
- Manufacturer-published bag yields, the same table the slab and post calculators use — only the volume formula ahead of the bag conversion changes between the three concrete calculators on this site.
Worked examples
A 4 step porch stoop, 3.5 ft wide
| Number of steps | 4 |
|---|---|
| Step width | 3.5 ft |
| Rise per step | 6.5 in |
| Run per step | 12 in |
| Concrete volume | 18.96 cu ft |
|---|---|
| Cubic yards | 0.7 cu yd |
| 80lb bags | 32 bags |
| 60lb bags | 43 bags |
| 90lb bags | 29 bags |
Four steps at this width, rise, and run come to 18.96 cu ft — 32 bags of 80 lb mix — with the triangular factor (4×5/2=10) meaning the bottom step alone carries roughly 40% of the total volume, since it's the only one supporting the full 26 inch stack height.
That uneven distribution is worth knowing before pricing per-step labor or forms: the bottom step of any flight is disproportionately expensive in material, and a stair with a shallow first riser (a common accessibility choice) shifts even more volume into that bottom pour.
A 6 step flight, same width, rise, and run
| Number of steps | 6 |
|---|---|
| Step width | 3.5 ft |
| Rise per step | 6.5 in |
| Run per step | 12 in |
| Concrete volume | 39.81 cu ft |
|---|---|
| Cubic yards | 1.47 cu yd |
| 80lb bags | 67 bags |
| 60lb bags | 89 bags |
| 90lb bags | 59 bags |
Adding two more steps to the same-shaped flight — a 50% increase in step count — more than doubles the volume, from 18.96 to 39.81 cu ft, because the triangular factor jumps from 10 to 21 (6×7/2), a 110% increase against the 50% growth in step count.
This is the nonlinear growth every taller staircase runs into: a 50% increase in step count here produced a 110% increase in concrete, not a matching 50%, which is worth budgeting for before assuming a slightly taller porch is only a slightly bigger pour.
Common mistakes
- Treating the whole staircase as one flat-topped rectangular volume (width x depth x total height), which significantly overstates real concrete needed since it ignores the stepped shape.
- Forgetting the footing/pad the steps sit on, which is its own volume separate from the steps themselves.
- Not checking rise/run against comfortable stair proportions before pouring — see how to calculate stair rise and run, since a poured concrete mistake here is far more expensive to fix than a framing mistake.
- Underestimating form-building complexity — stepped forms need more bracing than a flat slab form to resist the concrete's weight at each stepped level during the pour.
- Not planning the pour as one continuous placement — stopping partway through a stepped pour and resuming later can create a visible cold joint and a weaker bond between sections.
- Skipping a broom or non-slip finish on the tread surfaces, which is a real safety concern on outdoor steps independent of the volume calculation.
Shopping summary
Buy bags totaling the summed per-step volumes plus footing volume, rounded up, with 5-10% extra for form spillage; this is a structural pour on a walked surface — confirm the form design and rise/run with a professional before pouring.
Worked example: three steps, each 3 feet wide and 11 inches deep (run), with a 7-inch rise per step. Step 1 (bottom) volume ≈ 3 x (11/12) x (21/12) ≈ 4.8 cubic feet (full stack height of 21 inches beneath it). Step 2 ≈ 3 x (11/12) x (14/12) ≈ 3.2 cubic feet. Step 3 (top) ≈ 3 x (11/12) x (7/12) ≈ 1.6 cubic feet. Total ≈ 9.6 cubic feet, plus a footing pad — call it 12-14 cubic feet all in, or roughly 20-24 sixty-pound bags at 0.6 cu ft actual yield allowance.
FAQ
Do I need less concrete for steps than a slab of the same footprint?
Yes, meaningfully less — because only the actual stepped shape is solid concrete, not a full rectangular block up to the top step's height, treating it as a solid block would overstate the true volume by a wide margin.
Should the footing be poured separately from the steps?
It can be poured integrally in one continuous placement or separately with a cured joint, depending on the design — either way its volume is additional to the stepped volume above it and needs to be included in the bag count.
Can I pour concrete steps over an existing set of steps instead of demolishing them?
Sometimes, if the existing steps are structurally sound and a bonding agent is used to help the new pour adhere, but this is a case-by-case structural decision — a cracked, heaving, or undermined existing step is generally not a safe base to build over and should be removed first.
How many bags of concrete does a typical 3-step stoop need?
It varies with width and rise/run, but a modest 3-foot-wide, 3-step stoop commonly lands in the range of 20-30 sixty-pound bags including a footing pad — always run your own specific dimensions through the calculator rather than assuming a flat number, since width alone can shift that total substantially.
Where to go next
The projects this number is a step of, the guides that explain the method behind it, and the rest of its trade group.