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Diopter Calculator
Convert focal length to lens power in diopters, and back. Optical information only.
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Power from focal length
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Convert focal length to lens power in diopters, and back. Optical information only.
Diopter Estimator
Enter your numbers below for an instant estimate.
0
💡 Tip: D = 1 / f (metres).
How It Works
Key concepts behind this calculator
1
Enter Values
Fill in each field with your own numbers.
2
Calculate
Results update as you change the inputs.
3
Review
Read the breakdown and the explanation.
4
Adjust
Change values to compare scenarios.
Quick Reference Guide
Diopter Quick Guide
Typical values for reference.
| Focal cm | Power | Type | Type |
|---|---|---|---|
| 200 | 0.50 D | Converging | 0.50 D |
| 100 | 1.00 D | Converging | 1.00 D |
| 50 | 2.00 D | Converging | 2.00 D |
| 25 | 4.00 D | Converging | 4.00 D |
| Rule of Thumb | Check inputs | Use as a guide | Round sensibly |
Common Questions
Diopter Calculator FAQ
Answers to common questions about this calculator.
The unit of lens power, one over focal length in metres.
A diverging lens.
No, see an optician.
Thin lens powers add.