Concrete design tool
Concrete beam design calculator
Size a reinforced concrete beam step by step. We check bending, shear, bar spacing and depth against ACI 318-19 and show every formula with your numbers, so you can follow the work. A licensed PE can then review and seal it.
Preliminary design only. For planning and learning. Not for construction or a permit until a PE licensed in the project's state has reviewed and sealed it.
CivilEngineer.ai
Concrete beam calc package
Preliminary design only. For planning and learning. Not for construction or a permit until a PE licensed in the project's state has reviewed and sealed it.
We attach your inputs and our check to the request. A PE licensed in your state reviews it and replies with scope, fee and schedule. The calc package opens your print dialog: choose Save as PDF.
Load, shear and moment diagrams
Code checks
| Check | Value | Limit | ACI 318-19 | Result |
|---|
Full calculation
Every formula with your numbers substituted. Units: in, psi, kips and kip-ft.
Inputs
Assumptions and limits
- Normalweight concrete at 150 pcf, or lightweight concrete (sand-lightweight 120 pcf, all-lightweight 105 pcf, both including the bars) with λ from ACI 318-19 Table 19.2.4.1(b). The slab is taken as the same concrete. One layer of tension bars, no compression steel, no torsion.
- The factored load is the larger of 1.4D and 1.2D + 1.6L (ASCE 7 and ACI 318-19 section 5.3). No live load reduction is taken.
- Simple spans use wL²/8 and wL/2, cantilevers wL²/2 and wL. Continuous spans use the ACI 6.5 approximate coefficients, which need roughly equal spans, uniform load and live load no more than 3 times dead load.
- Shear is checked at distance d from the support face, with the simplified Vc = 2λ√f'c bw d where stirrups are provided.
- Cover follows ACI 20.5.1.3: 1.5 in indoors, 2 in for #6 and larger bars exposed to weather, 3 in cast against soil. Maximum aggregate 3/4 in.
- Deflection is calculated with the cracked section stiffness of ACI 318-19 Table 24.2.3.5 at midspan (at the support for a cantilever). Sustained load is the dead load plus 20 percent of the live load, with the 5 year creep factor of 2.0. Cantilever limits use twice the cantilever length.
- On continuous spans the uniform load deflection uses end moments that match the ACI coefficient moment, and point loads are treated as simply supported. Slab stiffness (T beam action) is ignored, which overestimates deflection.
- Point loads use exact statics on simple spans and cantilevers. On continuous spans each point load adds its simple span moment at midspan and its fixed end moment and reaction at the support, which is conservative.
- Not checked: bar development and splices, cutoff points, T beam action, torsion, connections and fire rating. A PE checks these before sealing.
Frequently asked questions
Can I build from this calculation?
No. It is a preliminary design for planning and learning. Building departments require structural drawings sealed by a PE licensed in the project's state, and the engineer also checks items this tool does not, such as bar development, splices and connections.
Which code does the calculator use?
ACI 318-19, Building Code Requirements for Structural Concrete, with load combinations from ASCE 7. Each check in the results names the ACI section it comes from.
Why does my beam need stirrups?
Concrete alone resists only part of the shear. Where the factored shear is more than half of the simplified concrete shear strength, ACI 318-19 section 9.6.3.1 requires at least minimum stirrups, and closer stirrups where the shear is higher.
What does the Table 9.3.1.1 minimum depth mean?
For beams that do not support partitions likely to be damaged by deflection, ACI lets you skip a deflection calculation when the beam is at least span/16 deep for a simple span, span/18.5 with one end continuous, span/21 with both ends continuous or span/8 for a cantilever. Shallower beams need calculated deflections.