Concrete Stair Calculator

How this concrete stair calculator works

This tool estimates how much concrete you need for a straight flight of uniform steps (plus an optional rectangular landing slab). It converts your inputs to consistent units, calculates the stair volume using a geometric “stair prism” model, adds any landing slab volume, then applies a waste allowance. Results are shown in cubic feet and cubic yards, with optional bag counts and an optional cost estimate if you enter a price per cubic yard.

Inputs (and units checklist)

• Number of steps (n) — count the risers (vertical faces). In many builds, this equals the number of treads, but confirm how your steps are formed.
• Riser height (r) — in inches (vertical height of one step).
• Tread depth (t) — in inches (horizontal depth of one step, excluding any nosing).
• Stair width (w) — in feet (overall pour width).
• Landing length (L) — in feet (optional; set to 0/blank if none).
• Landing thickness (h) — in inches (slab thickness of the landing only).
• Waste allowance (%) — typical 5–12% depending on forming accuracy and site conditions.
• Price per cubic yard — optional (enter the delivered ready-mix price per yd³ if you want a cost estimate).

Unit reminders: rise/run/thickness are entered in inches, while width/landing length are in feet. The calculator converts inches → feet internally.

Formulas used

Let:

• n = number of steps
• r = riser height (in)
• t = tread depth (in)
• w = stair width (ft)
• L = landing length (ft, optional)
• h = landing thickness (in)
• f = waste allowance (%)

Convert inches to feet:

• r_ft = r / 12
• t_ft = t / 12
• h_ft = h / 12

Total rise and run:

• R = n · r_ft
• T = n · t_ft

The stair volume is modeled as a right-triangular prism (a wedge):

If you include a rectangular landing slab:

• V_landing = w · L · h_ft

Subtotal and waste-adjusted volume:

• V_subtotal = V_stairs + V_landing
• V_final = V_subtotal · (1 + f/100)

Conversions:

• Cubic yards: yd³ = ft³ / 27

Bag count and yield assumptions

If you use bagged mix, the calculator estimates bag counts using common approximate yields:

• 80 lb bag ≈ 0.60 ft³ per bag
• 60 lb bag ≈ 0.45 ft³ per bag

Bag yields vary by manufacturer, mix design, and water content. For the most accurate plan, verify the yield printed on your specific bag and adjust your waste percentage accordingly.

Interpreting your results

• Cubic feet is useful for cross-checking against your measured geometry and for small pours.
• Cubic yards is how ready-mix is commonly ordered (often with minimum-load fees). Many contractors round up to the next 0.25 yd³ or 0.5 yd³ depending on supplier policy and access.
• Waste allowance covers spillage, over-excavation, uneven subgrade, form bulging, and small design details not captured by the simple geometry model.
• Cost estimate (if price is entered) is a material-only approximation; delivery, short-load fees, pumping, reinforcement, excavation, and finishing can materially change project cost.

Worked example

Example: 6 steps, 7 in riser, 11 in tread, 4 ft width, optional landing 3 ft long at 6 in thick, waste 5%.

• r_ft = 7/12 = 0.5833 ft
• t_ft = 11/12 = 0.9167 ft
• R = n·r_ft = 6·0.5833 = 3.5 ft
• T = n·t_ft = 6·0.9167 = 5.5 ft
• V_stairs = (1/2)·R·T·w = 0.5·3.5·5.5·4 = 38.5 ft³
• Landing volume: h_ft = 6/12 = 0.5 ft; V_landing = 4·3·0.5 = 6.0 ft³
• Subtotal = 44.5 ft³
• With 5% waste: V_final = 44.5·1.05 = 46.7 ft³
• In cubic yards: 46.7/27 = 1.73 yd³

Bag estimate (approx.):

• 80 lb bags ≈ 46.7 / 0.60 ≈ 78 bags
• 60 lb bags ≈ 46.7 / 0.45 ≈ 104 bags

If ready-mix is $135/yd³, estimated concrete material cost ≈ 1.73 · 135 ≈ $234 (excluding fees and labor).

Typical stair dimension guidance (comfort check)

A common rule of thumb for comfortable stairs is:

• 2r + t ≈ 24–25 inches

Always check local code requirements for stair geometry, landings, handrails, and slip resistance. This page provides estimating guidance, not code approval.

Limitations and assumptions

• Straight, uniform stairs only: turned stairs, winders, spiral stairs, and variable risers/treads are not modeled.
• Solid wedge approximation: the stair run is treated as a continuous triangular prism. Real formed steps may differ (e.g., voids, separate stringers, chamfers, architectural profiles).
• No thickened edges, curbs, or side walls: if your stairs include integral curbs/cheeks, retaining walls, or side stems, you must add that volume separately.
• Landing is a simple rectangle: assumes landing thickness is uniform and landing width equals stair width.
• Does not include subbase excavation or gravel: those are separate takeoffs.
• Does not subtract reinforcement volume: rebar/mesh volume is negligible for most estimates but is ignored here.
• Field conditions vary: slope, soil, form movement, and finishing methods can increase actual concrete used; adjust waste accordingly.