When to use this calculator
Convert a lens focal length in metres into optical power. An ideal optical quantity, not a prescription recommendation or eye assessment.
Explore the optics & quantum relationships calculators for other questions in this topic. For a related calculation, use the Photon Energy Calculator: Calculate the energy of a photon from its vacuum wavelength.
PUTTING IT INTO PRACTICE
Lens Power: a worked example
The values below are an illustrative example, not a recommendation. Replace them with measurements or assumptions that match your question.
| Input | Example value |
|---|---|
| Signed focal length (m) | 0.5 |
| Result | 2 dioptres |
- Check the input labels and enter the example values above.
- Apply the relationship: Optical power = 1/focal length in metres.
- The result is 2 dioptres, rounded for display.
How to interpret your result
An ideal optical quantity, not a prescription recommendation or eye assessment.
Use the stated sign convention for lenses and angles measured to the normal for refraction. Vacuum wavelength differs from wavelength inside a material. These models do not account for every optical aberration or material response.
Frequently asked questions
Why can a refracted-angle calculation have no real result?
When Snell’s-law sine exceeds one, the ideal ray model predicts total internal reflection rather than a real transmitted angle.
When is the lens power calculator useful?
Convert a lens focal length in metres into optical power. An ideal optical quantity, not a prescription recommendation or eye assessment.
How do I use the lens power calculator?
Enter signed focal length (m). The result updates automatically. Use the units shown beside each input; the example values illustrate the method.
Which formula does this calculator use?
Optical power = 1/focal length in metres.
What should I check before using the result?
An ideal optical quantity, not a prescription recommendation or eye assessment.
How are results rounded?
Scalar numbers display up to six decimal places, with scientific notation for very large or small values. Text, fraction, date and schedule outputs use the format described on the tool. Intermediate calculations use JavaScript floating-point arithmetic. Keep sensible precision for your measurements.
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