Calculator Inputs
Use consistent units; the tool converts internally.
Example Data Table
Use these sample cases to sanity-check your inputs.
| Support | Load | Span | E | Section | Deflection (approx.) |
|---|---|---|---|---|---|
| Simply supported | UDL 2.5 kN/m | 4.0 m | 11.0 GPa | 50 × 200 mm | ≈ 22.73 mm |
| Simply supported | Point 10 kN (midspan) | 4.0 m | 11.0 GPa | 50 × 200 mm | ≈ 36.36 mm |
| Cantilever | UDL 1.5 kN/m | 2.5 m | 10.0 GPa | 75 × 225 mm | ≈ 10.29 mm |
Formula Used
This calculator uses classic elastic beam theory with a prismatic section:
- I = b·h³ / 12 (rectangular section)
- σmax = |M|max · c / I, where c = h/2
| Support | Load case | Maximum deflection |
|---|---|---|
| Simply supported | UDL | δmax = 5·w·L⁴ / (384·E·I) |
| Simply supported | Midspan point load | δmax = P·L³ / (48·E·I) |
| Cantilever | UDL | δmax = w·L⁴ / (8·E·I) |
| Cantilever | End point load | δmax = P·L³ / (3·E·I) |
| Fixed-fixed | UDL | δmax = w·L⁴ / (384·E·I) |
| Fixed-fixed | Midspan point load | δmax = P·L³ / (192·E·I) |
Assumptions: constant E and I, linear response, small rotations, and loads applied slowly.
How to Use This Calculator
- Select a unit system and support condition.
- Choose a load case and enter service-level load values.
- Enter timber modulus E (or pick a preset).
- Provide section size or a custom I value.
- Select a deflection limit, then press Calculate.
If results exceed the limit, consider a deeper member, shorter span, or reduced load.