Measuring before you order concrete
Concrete is poured once. Get these two numbers right before you order, because a mid-pour top-up is expensive and rarely matches the first truck's mix.
Find your total rise
Measure plumb from the finished grade, patio, or slab you're leaving to the finished grade or landing you're arriving at. On an existing opening, drop a plumb line from the top edge to the ground below.
Measure the full clear width
Measure the entire concrete width, side form to side form — not just the walking path. This number multiplies straight through to your volume, so a few inches of error compounds fast.
Decide riser height, or let it auto-set
Leave it on Auto and the calculator targets a comfortable 7.5" riser, then rounds to a whole step count. If your project has a fixed riser requirement, switch to Custom and enter it directly.
Add a landing if the stair ends on a platform
If the top of the stair lands on a flat slab rather than the ground or an existing porch, enter its depth and thickness in Advanced so that volume gets added to your order.
The five formulas behind every result
Nothing on this page is a black box. Here's exactly what runs when you change a number.
Step Count
Total rise divided by your target riser height, rounded to the nearest whole step — you can't pour a fractional step.
Actual Riser Height
The rounding above means your real riser is rarely the exact target. This is the number every form board gets set to, uniformly.
Tread Depth (2R+T rule)
A standard comfort formula: twice the riser plus the tread should land near 24–25 inches. Floored at the 10" IRC minimum.
Concrete Volume (stepped-block method)
Sums each step as a stacked block rather than treating the stair as a smooth ramp — this is why the true figure runs higher than a naive Width × Rise × Run estimate.
Bag Count
Total volume including waste, divided by the yield of your selected bag size, rounded up to a whole bag.
Walking through a real 40" rise, 42" wide stair
Same five formulas, filled in step by step, for a 40" total rise entry stair at 42" clear width — the default this calculator loads with.
Step count
40" total rise, targeting a 7.5" riser: 40 ÷ 7.5 = 5.33, which rounds to 5 steps. You can't pour a fractional step, so the calculator always rounds to the nearest whole number here.
Actual riser height
Re-divide the total rise by that whole step count: 40 ÷ 5 = 8.0" per riser. That's already past the 7.75" IRC maximum — the riser chip below will flag it, which is a real, useful warning at this exact input, not a display bug.
Tread depth
Using the 2R+T comfort rule: 25 − (2 × 8.0) = 9.0", which is below the 10" IRC minimum, so the calculator floors it at exactly 10". The tread chip passes at that floor even though the underlying comfort formula wanted something shallower.
Concrete volume
With 5 steps at a 42" (3.5 ft) width, 8.0" (0.667 ft) risers and 10" (0.833 ft) treads: V = 3.5 × 0.667 × 0.833 × (5×6÷2) = 3.5 × 0.667 × 0.833 × 15 ≈ 29.2 cu ft (1.08 cu yd) before waste. Add the default 10% waste factor and you're ordering ≈ 32.1 cu ft, 1.19 cu yd.
Bags or ready-mix
At 32.1 cu ft with 60 lb bags (≈0.45 cu ft yield each), that's ≈ 72 bags — enough that ordering a small ready-mix load usually beats hand-mixing that many bags on site. The calculator doesn't hide that math from you; it's exactly what the bag-count result shows.
This is exactly why the riser chip can fail on a perfectly reasonable-looking input — an 8" riser feels like a small rounding artifact of "40 ÷ 5," but code measures the real number, not the target. Switching to a 6-step layout (Custom riser ≈ 6.67") brings both the riser and the resulting stair angle back into range.
Bag size, yield & concrete mix reference
What the bag-count result is built on, and the mix strength most exterior steps are specified at.
| Bag Size | Yield | Approx. Bags / cu yd | Best For |
|---|---|---|---|
| 40 lb | ≈0.30 cu ft [VERIFY] | ≈90 | Small patch jobs, a single step repair. |
| 60 lb | ≈0.45 cu ft [VERIFY] | ≈60 | DIY stairs under roughly 1 cu yd. |
| 80 lb | ≈0.60 cu ft [VERIFY] | ≈45 | Larger DIY pours — best $/cu ft of the bag sizes. |
| Ready-mix (truck) | Sold by the cu yd; supplier minimums vary [VERIFY] | — | Anything above roughly 1 cu yd. |
Bag yields are printed on the bag and vary by brand and mix design — treat the figures above as planning estimates, not a substitute for the label.
| Application | Recommended PSI | Air Entrainment | Notes |
|---|---|---|---|
| Interior steps, no freeze-thaw | ≈3,000 psi [VERIFY] | Not required | Standard residential mix. |
| Exterior steps, freeze-thaw climates | ≈4,000 psi [VERIFY] | 5–7% [VERIFY] | Required in most cold-climate jurisdictions. |
| Steps near driveways / vehicle-adjacent | 4,000+ psi [VERIFY] | Per local code | Confirm with your local building department. |
Reference only — confirm mix design and air-entrainment requirements against your local adopted code and climate zone before ordering.
IRC residential stair code, quick reference
This calculator checks your result against the two limits below. Full residential code also covers headroom, width and handrails — see the linked calculators for those.
| Element | Residential (IRC) | Commercial (IBC) |
|---|---|---|
| Max riser height | 7.75" | 7" |
| Min tread depth | 10" | 11" |
| Riser variance across a flight | 3/8" | 3/8" |
| Min headroom | 6'8" | 6'8"–7'6" (varies) |
| Min clear width | 36" | 44"+ (varies) |
These figures match the Stair Rise and Run Calculator's code reference — reference only, always confirm against your local jurisdiction's adopted code before pouring.
Forming, base prep & curing
A stair can pass every riser and tread check and still crack or heave within a year over three things this section covers — sub-base prep, form/cure timing, and joints.
Compacted sub-base
Concrete steps poured directly on undisturbed or loose soil are the single most common cause of cracking and settling. A compacted gravel base gives uniform support and drainage under the full footprint — confirm depth against your soil type and local frost line.
Form strip & cure timing
Forms typically come off once the concrete can hold its own edges; light foot traffic usually waits several days longer, and full design strength isn't reached until roughly 28 days. Rushing traffic on new steps is a common cause of surface spalling.
Expansion / control joints
Where the stair meets an existing slab, foundation wall, or porch, an isolation joint lets the two structures move independently. Skipping it is a common cause of a crack running straight across the bottom step where it meets the walkway.
Reinforcement
Taller stairs and longer unsupported spans generally need rebar or welded wire mesh to control cracking — this calculator handles volume and forming only. Use the linked Rebar Calculator for bar size, spacing, and layout.
These are planning-stage estimates, not a stamped structural design. A tall stair, poor soil, or a heavy finish load may need an engineer's sign-off regardless of what this calculator shows.
Common mistakes when planning concrete steps
Most cracked, settled, or under-ordered concrete stairs trace back to one of these five planning errors, not to bad pouring technique.
Skipping the compacted sub-base
Pouring straight onto loose or undisturbed soil is the most common cause of a step that cracks or settles within the first year or two.
Estimating volume as Width × Rise × Run
That treats the stair like a solid ramp. Real stepped concrete is smaller than that box but larger than a simple triangle — use the stepped-block formula above, not a flat box estimate.
Missing the isolation joint at tie-ins
Where new steps meet an existing slab, porch, or foundation, skipping an expansion joint is a common cause of a crack running straight across the bottom step.
Stripping forms or loading traffic too early
Removing side forms before the edges can hold their shape, or letting foot traffic on before the surface has cured enough, commonly shows up later as chipped nosings and surface spalling.
Ordering bags without checking the ready-mix breakeven
Running out of bags mid-pour means a cold joint where the new batch meets the old — check the bag count against a ready-mix minimum order before you commit to hand-mixing.
When to use a concrete stairs calculator
Concrete step planning shows up anywhere a stair needs to be permanent, load-bearing, and poured once.
New Entry or Porch Steps
Sizing the pour for a front, back, or side entry before ordering concrete.
Replacing Cracked or Settled Steps
Tearing out an old failed pour and replacing it with a properly based one.
Basement & Garage Walkouts
Fitting a durable, code-compliant stair into an exterior walkout opening.
Pool Deck & Patio Steps
Planning steps between a patio and a lower or raised pool deck area.
Commercial Storefront Entries
Estimating volume for a contractor bid on a small commercial entry stair.
DIY Driveway or Garden Steps
Bag-count planning for a weekend concrete pour without a ready-mix order.