Free tool · runs in your browser
Continuous Beam Design Calculator — SFD, BMD & ACI 318 Check
Free continuous beam calculator: up to 6 spans, pinned/roller/fixed/cantilever supports, area or line loads — draws the shear force & bending moment diagrams, then sizes rebar and stirrups per ACI 318-19.
No signup · nothing uploaded · Free — unlimited use, everything runs in your browser; no structural model is uploaded
How it works
Define the spans
Up to 6 spans with individual lengths; remove spans to merge supports.
Set the supports
Pinned, roller, or fixed at each node — free ends create cantilevers.
Enter the loads
Area loads (psf × tributary width) or line loads (klf), plus optional point loads.
Read the diagrams
Beam elevation, SFD, BMD, reactions, and the governing load combination.
Size the concrete
Section dimensions and material strengths → rebar, εt, and stirrups per ACI 318-19.
Enter your spans, supports, and loads and this calculator solves the continuous beam with a real stiffness-method engine — not the simplified coefficient tables — then draws the shear and moment envelopes, reports every support reaction, and finishes with an ACI 318-19 reinforced-concrete design: required steel area per span and support, a suggested rebar pick, net tensile strain, and shear stirrups. Optional self-weight (150 pcf) is added to dead load automatically.
It handles what the quick-reference tables can't: unequal span lengths, cantilever overhangs, fixed ends, point loads anywhere on the beam, the ASCE 7 load combinations (1.4D, 1.2D + 1.6L + 0.5Lr, 1.2D + 1.6Lr + 1.0L), and — critically for continuous beams — ACI 6.4.2 live-load patterning, so the envelopes show the true worst case of every combination and skip-loading arrangement. Everything runs in your browser — no model data is uploaded.
Questions, answered
A beam that spans over more than two supports — for example a floor beam continuous over three columns. Continuity creates negative (hogging) moments over the interior supports and reduces the positive (sagging) midspan moments compared with a series of simply-supported spans, which is why continuous framing is more material-efficient.
More free tools
Need more than the free limit?
In PDFDepth, Engineering Mode reads the beam schedule and span callouts straight off the structural PDF, and the built-in Design Check runs the analysis on the drawing itself — no re-typing dimensions.
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