Concrete Calculator: Stairs (Straight Run) Volume & Tread/Riser Layout

Plan straight-run concrete stairs fast. Enter stair width, total rise, number of risers, tread depth (going), and number of treads. Optionally include a landing slab and a waste allowance. You’ll get actual riser height, total run length, the 2R+T check, concrete volumes in m³ / yd³ / ft³, and approximate bag counts. Notes, formulas, and FAQs are included.

Units Metric (m, mm) US Customary (ft, in)

Stair width

Total rise (floor-to-floor)

Number of risers

pcs

Typical straight flights use 12–16 risers depending on floor height.

Tread depth (going)

Number of treads

pcs

Often equals number of risers. If your top landing is the final “tread”, set them equal.

Waste allowance

Covers overbuild, spillage, and dimensional variation (common 4–10%).

Add a landing slab (optional)

Landing depth

Landing thickness

Landing is assumed the same width as the stairs.

Layout helper (optional)

Target riser height

Target 2R+T

Blondel’s rule of thumb: 2 × riser + going ≈ 600–650 mm (≈ 24–25.5 in).

Results

Actual layout

Riser height: 0 mm

Total run length: 0.000 m

2R+T check: 0 mm

Stair volume (wedge)

0.000 m³

0.000 yd³

0.00 ft³

Landing volume

0.000 m³

0.000 yd³

0.00 ft³

Total with waste

0.000 m³

0.000 yd³

0.00 ft³

Approximate bag counts (total with waste)

US bag sizes (QUIKRETE® yield)

40 lb bag00.30 ft³ per bag

50 lb bag00.375 ft³ per bag

60 lb bag00.45 ft³ per bag

80 lb bag00.60 ft³ per bag

90 lb bag00.675 ft³ per bag

Yields per bag from QUIKRETE data sheet. Actual yield varies with placement and compaction. Source

Metric bag sizes

Edit yields to match your local supplier data.

20 kg bag yield m³ 25 kg bag yield m³ 40 kg bag yield m³

20 kg bag0

25 kg bag0

40 kg bag0

How to use this stairs calculator

Select metric or US units.
Enter stair width and total rise (floor-to-floor height).
Enter number of risers, tread depth (going), and number of treads. (Often treads = risers if the top landing is the final tread.)
Optional: add a landing slab (depth and thickness).
Set a waste allowance (many projects use 4–10%).
Review the results: actual riser height, run length, 2R+T check, volumes, and bag counts. Round up for ordering.

Formulas and assumptions

Riser height: h = H / n_risers, where H is total rise.
Total run: R = n_treads × G, where G is going (tread depth).
Stair volume (solid wedge): Treat the flight as a right triangular prism of width W, run R, rise H:
V_stairs = (W × R × H) / 2
Equivalent to summing rectangular “step” blocks: V = W × G × h × n(n+1)/2 (same result).
Landing volume: V_landing = W × D × T (with D depth, T thickness).
Total with waste: V_total,w = (V_stairs + V_landing) × (1 + w%).
2R+T rule check (Blondel): 2h + G should be in about 600–650 mm (≈24–25.5 in) for comfortable stairs. This is a guideline, not a code requirement.
Scope: Volume only. This does not size reinforcement, stringers, or code compliance for risers/treads/handrails. Always follow your engineer and local building code.

References

Blondel’s rule (2R+T ≈ 63 cm): see stair design literature (e.g., Stairs—design).
Typical code limits (verify your jurisdiction): IRC (residential) commonly ≤7.75 in riser, ≥10 in tread; IBC (commercial) commonly 4–7 in riser, ≥11 in tread (consult current code text). ICC.
Concrete waste allowance ~4–10%: NRMCA Concrete In Practice CIP 8, CIP 31.
US bag yields: QUIKRETE® Concrete Mix 1101 data sheet.

FAQs

Should treads equal risers?

Often yes for a single flight where the top landing acts as the final “tread.” If your layout differs, set treads and risers to match your drawings.

Does this assume solid concrete?

Yes—this model treats the stair flight as a solid wedge. For a thin sloping slab over infill, the result is usually similar. For hollow or precast systems, volumes differ.

What if my run or rise must match code limits?

Use the Layout helper to suggest risers and going based on your total rise and target 2R+T, then adjust to meet your local code and engineer’s design.