Concrete Stairs Calculator
Volume, Bags & Cost
Calculate the exact cubic yards, bag count, and material cost for poured-in-place concrete stairs. Enter step count, rise, run, and width: the calculator handles the stair geometry and outputs the volume with optional landing slab. Includes IRC stair dimension guide and rebar reference.
Know your stair volume before you order concrete. Enter your step dimensions to get cubic yards, bag count, and a ready-mix vs bagged cost comparison instantly.
IRC max 7.75" rise, 4 steps = 28" total rise at 7"
IRC max 7.75" residential. Most common: 7"
IRC min 10" residential. Most common: 11"
Clear width in feet. IRC min 3 ft residential.
Optional top or bottom landing, 4" thick assumed. Enter 0 to skip.
10% recommended: stair geometry absorbs more than theoretical
National avg $165–$210/CY. Add $50–$200 short-load for small pours.
Enter step count, rise, run, and width
to calculate concrete volume
Related Construction Calculators
More tools for your concrete and construction projects
The concrete stair volume formula
Poured concrete stairs form a stepped triangular prism. Each step you add raises the entire staircase by one increment, so the lowest step carries the most concrete, it must support the volume of all steps above it. The formula accounts for this stacking geometry correctly.
Stair Volume (no landing)
CY = Width ft × Run ft × Rise ft × n(n+1)/2 ÷ 27 × 1.10
Landing Slab Volume (add separately)
CY = Length ft × Width ft × 0.333 ft (4") ÷ 27
The n(n+1)/2 term is the triangular number for n steps: it captures the stacking geometry without any iterative calculation. For 5 steps: 5×6/2 = 15. For 4 steps: 4×5/2 = 10. This formula treats each step as a rectangular prism of run × rise × width stacked above the previous one, which correctly models how poured stairs fill the formwork. The 1.10 multiplier applies the ACI-recommended 10% overage.
A worked example: 4 steps at 7-inch rise, 11-inch run, 4-foot width. V = 4 × (11/12) × (7/12) × (4×5/2) / 27 × 1.10 = 4 × 0.917 × 0.583 × 10 / 27 × 1.10 = 0.873 CY. That is approximately 40 bags of 80lb mix. Add a 4×4-foot landing at 4 inches: 4 × 4 × 0.333 / 27 = 0.198 CY extra. Total order: 1.07 CY. Use the concrete slab calculator if your landing slab is a separate, larger pour combined with an approach slab.
IRC stair dimension guide
The IRC 2024 Section R311.7 governs residential stair geometry. Every dimension affects the concrete volume, even a 1-inch change in rise on a 6-step stair changes the pour volume by 8 to 12%. Understanding the code limits before designing is essential to avoid having to re-form and re-pour.
| Dimension | IRC Minimum | IRC Maximum | Common Design |
|---|---|---|---|
| Rise per step | 4" | 7.75" | 7" |
| Run per step | 10" | No max | 11" |
| Clear stair width | 36" | No max | 36–48" |
| Headroom clearance | 6’–8" | No max | 7’+ |
| Rise variation (max) | ⅜" between any two steps | <⅜" | |
| Landing depth (min) | 36" | No max | 36–48" |
The 3/8-inch maximum variation rule between any two steps is the most commonly failed inspection item on residential stair pours. Uneven formwork, settling before the pour sets, or trowelling the top surface of risers to adjust appearance can all create a step that exceeds the 3/8-inch limit. Measure every step after form removal and before the inspector arrives, remediation after the fact typically requires grinding (which creates surface damage) or a patching compound that will likely crack within a season.
For exterior entry stairs, the common design is a 6-inch rise and 12-inch run: shallower than the IRC interior maximum to make the approach more gradual and reduce ice accumulation on the nosing. The concrete footing calculator can help size the footing under the stair base if required by your local jurisdiction.
Volume by step count
The table below gives concrete volume for common residential stair configurations at 7-inch rise and 11-inch run (the most common design) at 4-foot and 5-foot widths. All values include 10% overage and use the stepped triangular prism formula. A landing slab is not included.
| Steps | Total Rise | 4 ft wide | 5 ft wide | Bags (4 ft) |
|---|---|---|---|---|
| 3 | 21" | 0.52 CY | 0.65 CY | 24 bags |
| 4 | 28" | 0.87 CY | 1.09 CY | 40 bags |
| 5 | 35" | 1.31 CY | 1.63 CY | 59 bags |
| 6 | 42" | 1.83 CY | 2.29 CY | 83 bags |
| 7 | 49" | 2.44 CY | 3.05 CY | 110 bags |
The break-even between bagged and ready-mix concrete falls at roughly 1.5 cubic yards once short-load delivery fees are included. A 4-step stair at 4 feet wide (0.87 CY) is solidly a bagged concrete job, 40 bags, manageable with a small mixer or in batches. A 6-step stair at the same width (1.83 CY) is borderline , factor in the short-load fee from your ready-mix plant before deciding. A 7-step stair at either width exceeds 2.4 CY, where ready-mix almost always wins on both cost and labour. The calculator shows the exact cost comparison for your dimensions and local pricing.
Rebar and forming
Poured concrete stairs require reinforcement to resist the cracking that results from differential settlement between the stair base and the structure it connects to. The base of the stair sits on the ground or a footing; the top rests against the landing slab or foundation wall. Any movement between these support points (seasonal ground movement, settling, frost heave) applies shear and bending stress through the stair body. Without rebar, the unreinforced concrete will crack at the base.
| Location | Bar size | Spacing | Purpose |
|---|---|---|---|
| Base slab | No. 4 | 12" each way | Flexural reinforcement in base |
| Nosing bars (longitudinal) | No. 4 | 18" OC along width | Prevent nosing chipping and spalling |
| Riser bars (cross bars) | No. 3 or No. 4 | 1 per step | Tie nosing bars together |
| Wall-to-stair dowels | No. 4 | 24" OC | Connect base to foundation wall |
The nosing bars are the most commonly omitted element on residential stair pours. The leading edge of each step (the nosing) takes direct impact from foot traffic and is exposed on three sides to moisture infiltration. Unreinforced nosings chip and spall within 3 to 5 years in climates with freeze-thaw cycling, and the repair (patching with cementitious material) rarely lasts more than one winter. Placing a No. 4 bar 1 to 1.5 inches back from the nosing edge on every step prevents this failure mode entirely at a material cost of roughly $15 for a typical residential stair.
Stair forms are labour-intensive to build correctly. The vertical riser boards must be held perpendicular to the sloped soffit, and each form board must be braced against the hydrostatic pressure of fresh concrete. A common field failure is the bottom form board blowing out during the pour, which dumps concrete at the base and leaves voids in the step above. Brace every riser form at two points minimum and check the bracing after placing the first bucket of concrete before continuing.
Pour sequence for concrete stairs
The pour sequence for concrete stairs is bottom to top, this is the single most important technique point for a stair pour and the opposite of what feels intuitive. Pouring from the top allows concrete to flow down and fill the forms unevenly. The weight of fresh concrete above can blow out lower forms before they have time to stiffen. Starting from the bottom and working up gives the lower pours a few minutes to begin stiffening before the upper concrete is placed against them.
For a 4 to 6 step residential stair using bagged concrete, the practical sequence is: mix two or three bags and fill the bottom step to full depth, consolidate with a rod or small vibrator, then move up. Each step should be screeded to the top of the riser form and the surface finished to a broom finish while still workable. The broom finish serves two purposes: it creates the slip-resistant texture required by code and it removes the bleed water sheen that causes premature surface cracking if finished too early or too late.
Do not use a vibrator on stair pours at high speed or for extended periods: the vibration can cause the fresh concrete to flow under the riser forms and create voids. A rod or low-frequency vibrator used briefly at each step is sufficient for consolidation. For ready-mix pours, have your crew and equipment staged before the truck arrives, there is no time to set up mid-pour and ready-mix stiffens faster in the deep base section where heat builds up from the large mass of concrete.
Reading your concrete stair result
Your result shows the total concrete volume for the stair run at the specified dimensions. Concrete stairs are typically poured monolithically with the landing slab, if your stair connects to a concrete landing, add the landing volume separately and order as one combined pour. For a standard 3-foot-wide exterior stair with 4 risers at 7 inches and a 10-inch tread, total volume runs approximately 0.3–0.5 cubic yards: within bagged concrete range if you have mixing capacity.
ACI 318-25 and most residential codes require a minimum of 3,000 PSI concrete for exterior stairs exposed to freeze-thaw cycles, with a maximum water-cement ratio of 0.45. Using 2,500 PSI mix on exterior stairs in freezing climates produces spalling within 2–3 winters. If your pour is under 0.5 CY, 80 lb bags of 4,000 PSI fiber-reinforced concrete mix are a practical choice and eliminate the short-load fee risk. Over 1.0 CY, ready-mix with air entrainment specified at 5–7% is the professional standard for freeze-thaw durability.
Frequently asked questions
How do I calculate concrete for stairs?
Use the stepped triangular prism formula: V = Width (ft) × Run (ft) × Rise (ft) × n(n+1)/2 ÷ 27 × 1.10. For 5 steps at 7" rise, 11" run, 4 ft wide: V = 4 × (11/12) × (7/12) × 15 / 27 × 1.10 = 1.31 CY. That is approximately 59 bags of 80lb mix. Add landing slab volume separately if present. The calculator above handles all unit conversions.
What is the standard rise and run for concrete steps?
IRC R311.7 sets maximum rise at 7.75 inches and minimum run at 10 inches for residential stairs. The most comfortable design is a 7-inch rise and 11-inch run, which satisfies the ergonomic rule that 2×rise + run ≈ 25 inches. Exterior entry stairs often use a 6-inch rise and 12-inch run for a more gradual approach. All steps in a flight must have uniform rise and run: the maximum variation allowed between any two steps is 3/8 inch.
How much concrete does a typical set of stairs use?
A 3-step stair at 7" rise, 11" run, 4 ft wide requires approximately 0.52 CY (24 bags). A 5-step stair requires approximately 1.31 CY (59 bags). A 7-step stair requires approximately 2.44 CY (110 bags), where ready-mix becomes more practical than bagged concrete. The break-even between bagged and ready-mix is roughly 1.5 CY once short-load delivery fees are included. The calculator provides exact volumes and cost comparisons for your specific dimensions.
Do concrete stairs need rebar?
Yes. Poured concrete stairs require No. 4 rebar at 12-inch centers in both directions within the base slab section, plus nosing bars along the leading edge of each step. The nosing bars are the most commonly omitted element, without them, the unreinforced nosing chips and spalls within a few years in freeze-thaw climates. Wall-to-stair dowels connect the base to the foundation wall and prevent the stair from separating under differential settlement.
How thick should a concrete stair slab be?
The base structural slab under a residential entry stair should be a minimum of 6 inches thick for stairs with 5 or fewer steps, and 8 inches for taller stairs or those subject to heavier loads. Individual step tread depth is set by the run dimension (10 to 12 inches typically). Step thickness is not a code-specified dimension: structural performance depends on base slab thickness and rebar placement within it, not the individual step profile.
Can I pour concrete stairs in sections?
It is technically possible but strongly discouraged for structural stairs. A cold joint between sections is a plane of weakness, differential settling will crack the connection. The correct approach is to pour the entire flight in one continuous pour from bottom to top. For a standard 3 to 7 step residential entry stair, the volumes are easily managed in a single pour. If sections are unavoidable, a structural engineer must design keyed construction joints with shear dowels.
How long does concrete take to cure on stairs?
Concrete stairs are safe for light foot traffic after 24 to 48 hours. Forms can be stripped after 24 hours in warm weather and 48 to 72 hours in cool weather. Keep the surface moist for 7 days per ACI 308R curing requirements: a wet burlap cover works well on exterior stairs. Do not allow heavy loads or vehicle access for at least 7 days. In cold weather (below 40°F), protect with insulating blankets until the concrete reaches 3,500 PSI per ACI 306R cold-weather guidelines.
References
American Concrete Institute. (2025). ACI 318-25: Building Code Requirements for Structural Concrete. ACI.
American Concrete Institute. (2016). ACI 308R-16: Guide to External Curing of Concrete. ACI.
International Code Council. (2024). International Residential Code, Section R311.7. Stairways. ICC.
RSMeans. (2025). Residential Cost Data. Gordian.