Concrete Stairs Volume Calculator
This calculator estimates the concrete required for a straight flight of poured stairs plus an optional landing. It models the stair flight as a triangular prism (side profile) and adds a rectangular landing when specified. Results include cubic feet, cubic yards, estimated weight, and a bag-equivalent.
Use the waste allowance to add a practical over-order percentage for site waste, slumping, finishing loss, or minor measurement uncertainty. Density and bag weight are configurable to reflect different concrete mix types or bag sizes.
Inputs
Results
Total horizontal run (ft)
5.8333
Total rise (ft)
4.375
Gross concrete volume (ft³)
38.2813
Volume including waste allowance (ft³)
42.1094
Concrete required (yd³)
1.5596
Estimated weight (lb)
6,316.4063
Number of bags (bag weight set below)
105
| Output | Value | Unit |
|---|---|---|
| Total horizontal run (ft) | 5.8333 | ft |
| Total rise (ft) | 4.375 | ft |
| Gross concrete volume (ft³) | 38.2813 | ft³ |
| Volume including waste allowance (ft³) | 42.1094 | ft³ |
| Concrete required (yd³) | 1.5596 | yd³ |
| Estimated weight (lb) | 6,316.4063 | lb |
| Number of bags (bag weight set below) | 105 | — |
Visualization
Methodology
The flight is approximated as a triangular prism: the side-profile triangle has base equal to total horizontal run (steps × tread) and height equal to total rise (steps × riser). Volume = 0.5 × total run × total rise × stair width.
If a landing is present, it is modeled as a rectangular slab: volume = landing length × stair width × landing thickness. The calculator sums both volumes, applies a user-specified waste allowance, converts to cubic yards (1 yd³ = 27 ft³), and multiplies by concrete density to estimate mass.
Default density (150 lb/ft³) reflects normal weight concrete; adjust for lightweight mixes or high-density aggregates. Bag-equivalent is calculated by dividing total weight by the bag weight entered.
Further resources
External guidance
Expert Q&A
Why is the stair modeled as a triangle?
A monolithic poured stair flight forms a triangular side profile when risers stack progressively. Modeling the side profile as a triangle and extruding by stair width yields a reliable volume estimate for solid stairs. Use the landing slab addition for flat landings.
What waste percentage should I use?
Common practice is 5–15% depending on site conditions, finishing losses, and mix handling. For complex forms or heavy reinforcement, choose the higher end. This calculator uses 10% by default.
What density should I use?
Normal-weight concrete is approximately 145–155 lb/ft³; 150 lb/ft³ is a conservative default. Adjust downward for lightweight mixes or upward for heavy aggregates. For specification-backed values consult technical resources from agencies or material suppliers.
Is this sufficient for ordering ready-mix?
This provides a planning estimate. Add the recommended overage and confirm with your supplier (they may require rounding or minimum truck quantities). For final ordering, share plans and site constraints with the ready-mix provider.
Can the calculator handle curved or spiral stairs?
No. This tool is for straight flights approximated as a triangular prism. For curved, spiral, or multi-flight stairs, perform a more detailed breakdown by segment or consult a structural engineer.
Are safety and regulatory considerations included?
This calculator estimates material quantities only. Follow OSHA and local building codes for formwork, access, reinforcement, and worker safety. See the cited regulatory resources for guidance on safe handling and construction practices.
Sources & citations
- NIST — Metric and SI Units (reference for unit consistency) — https://www.nist.gov/pml/weights-and-measures/metric-si-units
- OSHA — Construction (regulatory guidance for concrete work and site safety) — https://www.osha.gov/construction
- MIT OpenCourseWare — Materials / Civil engineering resources (material properties reference) — https://ocw.mit.edu
- Federal Highway Administration — Concrete Pavement and Materials resources — https://www.fhwa.dot.gov/pavement