Load Calculator
Estimate the support reactions, maximum shear, and peak bending moment on a simply-supported or cantilever beam under a uniform or point load — a quick first-pass check for joists, headers, and balconies before you size a member.
How to Use
- Pick the beam type — simply-supported or cantilever, with a distributed or point load.
- Enter the span in feet (the clear distance between supports, or the cantilever length).
- Enter the load magnitude and choose the unit: total pounds for a point load, or lb/ft for a distributed load.
- Read the support reactions and the maximum bending moment.
- Use the Show Work and Formulas below to see how the result was derived.
Show Work
Formulas
About the Load Calculator
Load Calculator is a quick, free tool for building, materials estimation and site work. It works in your browser and keeps everything on your device. Estimate the support reactions, maximum shear, and peak bending moment on a simply-supported or cantilever beam under a uniform or point load — a quick first-pass check for joists, headers, and balconies before you size a member.
How it works
Enter your figures and the result appears instantly, updating the moment you change anything. There is no submit button and nothing to wait for, so it is easy to try a few what-if numbers and compare the results. Just check each box holds the kind of value it expects.
Want the deeper story? The Knowledge Base explains the ideas behind the tools in more detail.
Frequently Asked Questions
Is this calculator code-compliant?
No — it is a quick estimator for the statics of a single beam, not a substitute for engineering. Real framing has to account for material strength, deflection limits, live and dead loads, combinations, and connections. Any load-bearing structure should be sized and stamped by a licensed structural engineer.
What is the difference between a distributed and a point load?
A distributed load spreads weight evenly along the beam (entered in lb/ft) — like a floor or roof bearing across a joist. A point load is a single concentrated force at one spot (entered in total pounds) — like a post or a column landing on a beam. They produce very different moment and reaction patterns, so pick the one that matches your situation.
What does the maximum bending moment tell me?
The bending moment is the internal force trying to bend the beam, and its peak value is where the beam is most likely to fail. You compare that moment against a member's allowable capacity (its section modulus times the material's allowable stress) to see if a given size and species is strong enough. A bigger or deeper beam carries more moment.
Why does a cantilever produce a bigger moment than a simple beam?
A cantilever is fixed at one end and free at the other, so the entire load is resisted at the single support — there is no second support to share it. For the same span and load, a cantilever's moment at the wall is much larger than a simply-supported beam's midspan moment, which is why cantilevered balconies need stout framing.
Does this account for deflection or bounce?
No. This tool only solves for reactions, shear, and moment (strength). Floors that feel bouncy usually fail a deflection or vibration check, not a strength one, and that depends on the beam's stiffness and the species' modulus of elasticity. Always check deflection separately when comfort matters.
How do I use the Load Calculator?
Simply type your numbers and read the result, which refreshes the instant you change something. There is nothing to submit and nothing to wait for.
Does it cost anything or need an account?
No. The tool is completely free, there is no account to create, and it keeps working offline after the page first loads.
Is anything I type uploaded?
No. The tool works entirely on your device, so the values you enter never leave your browser.
Common Use Cases
First-pass check on a header
Estimate the moment over a door or window opening before sizing the header in a span table.
Checking a floor joist
See the reactions and moment from a distributed floor load to sanity-check a joist span.
Sizing a cantilever balcony
Find the large support moment a cantilevered deck or balcony develops at the wall.
Understanding a point load
See how a concentrated load from a post above changes the reactions and peak moment on a beam.
Learning beam statics
Compare the textbook formulas for simple and cantilever beams with the step-by-step Show Work.
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