Calculated results
Your Kuhn length estimate will appear here after calculation.
Calculator inputs
Choose an estimation path and keep all length inputs in the same unit.
Plotly graph
The chart compares key length-scale outputs for the current estimate.
Formula used
The calculator offers several standard polymer-physics estimation routes. Use the route that matches the data you already have.
These relations are most useful for idealized freely jointed or worm-like chain estimates. Real systems can deviate because of solvent quality, branching, electrostatics, temperature effects, and excluded-volume behavior.
How to use this calculator
- Choose the estimation method that matches your available polymer measurement data.
- Pick one working unit and keep every length input in that same unit.
- Enter contour length, RMS distance, radius of gyration, persistence length, or segment count as required.
- Click Estimate Kuhn length to show the result panel above the form.
- Review the derived persistence length, segment count, flexibility ratio, and predicted chain dimensions.
- Use the CSV or PDF buttons to export the current output summary for reports or notes.
Example data table
| Method | Contour L (nm) | Measured input | Kuhn length b (nm) | Persistence lp (nm) | Segments N |
|---|---|---|---|---|---|
| Contour + RMS end-to-end | 1000 | 173.21 | 30.00 | 15.00 | 33.33 |
| Contour + radius of gyration | 1200 | 77.46 | 30.00 | 15.00 | 40.00 |
| Persistence length | 960 | 12.00 | 24.00 | 12.00 | 40.00 |
| Contour + segment count | 900 | 30.00 segments | 30.00 | 15.00 | 30.00 |
FAQs
What does Kuhn length represent?
Kuhn length is the effective freely jointed segment length of a real polymer chain. It compresses local stiffness into an equivalent segment size that reproduces large-scale chain dimensions.
When should I use the end-to-end method?
Use it when you know contour length and root-mean-square end-to-end distance. It is suitable for ideal-chain style estimates where the chain behaves like a random coil on larger scales.
When is the radius of gyration method useful?
Choose it when scattering or simulation work gives radius of gyration. The calculator back-calculates Kuhn length from the ideal-chain relation between contour length, gyration radius, and segment size.
Why is Kuhn length twice the persistence length here?
For worm-like chains, Kuhn length is commonly approximated as two persistence lengths. This converts local bending stiffness into an equivalent freely jointed model for larger-scale analysis.
Do all inputs need the same unit?
Yes. Keep contour length, persistence length, end-to-end distance, and radius of gyration in one consistent unit. The calculator keeps the same unit in all returned length results.
Can this replace detailed polymer simulations?
No. It is an estimator for quick design checks, teaching, and first-pass analysis. Solvent quality, excluded volume, branching, charge effects, and architecture can change real behavior.
What does the segment count mean?
Segment count equals contour length divided by Kuhn length. Larger counts imply more effective segments and usually more coil-like large-scale behavior than short, rod-like chains.
Why are predicted coil dimensions shown?
They help you compare the estimated Kuhn length against implied chain size. Seeing predicted root-mean-square extension and radius of gyration makes the estimate easier to interpret.