Simply Supported Beam Deflection Calculator
Estimate the idealized elastic midspan deflection for a common beam loading case. The tool shows the method and key assumptions so you can inspect how the input values lead to the estimate.
How to use this calculator
- Enter central point load (n) using the unit and definition shown beside the input.
- Enter clear span (mm) using the unit and definition shown beside the input.
- Enter elastic modulus (mpa, n/mm²) using the unit and definition shown beside the input.
- Check that all values refer to the same time period and scenario.
- Review the outputs alongside the assumptions before using them in a decision.
Formula and assumptions
For a simply supported beam with a central point load, midspan deflection δ=PL³/(48EI).
- Assumes a prismatic, linearly elastic beam, small deflection, simple supports and a central point load. It omits shear deflection, self-weight, load combinations, lateral stability and code checks.
- The estimate is calculated from values you enter. It does not connect to external accounts, obtain live prices, or validate local regulations or engineering specifications.
Worked examples
Worked example
A 1,000 N central load over a 3,000 mm span with E=200,000 MPa and I=8,000,000 mm⁴ gives about 0.352 mm deflection.
Use consistent mm, N, N/mm² and mm⁴ units.
This simplified estimate is not a substitute for structural design, applicable standards or a qualified engineer.
Understanding the result
Assumes a prismatic, linearly elastic beam, small deflection, simple supports and a central point load. It omits shear deflection, self-weight, load combinations, lateral stability and code checks.
Change one input at a time to see how sensitive the output is to that assumption.
Important notes
Assumes a prismatic, linearly elastic beam, small deflection, simple supports and a central point load. It omits shear deflection, self-weight, load combinations, lateral stability and code checks.
Frequently asked questions
What formula does the Simply Supported Beam Deflection Calculator use?
For a simply supported beam with a central point load, midspan deflection δ=PL³/(48EI).
What should I verify before relying on the result?
Assumes a prismatic, linearly elastic beam, small deflection, simple supports and a central point load. It omits shear deflection, self-weight, load combinations, lateral stability and code checks.
Can I compare different scenarios?
Yes. Change one assumption at a time, keep units and definitions consistent, and save the inputs used for each comparison.
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This page provides a calculation tool plus explanatory information so you can understand what the result means and when the underlying method may not fit your situation.