Focal length in millimeters to diopters
Type a value in mm to get it in D instantly.
500D
That's 2× as strong as a microscope objective — nothing on our list beats it. That brings light to a focus about 2 mm away.
Convert the other way: D to mm
What it means
How strong is that lens?
Prescriptions carry a cylinder and an axis as well, for astigmatism. This page converts the sphere, which is the main number.
The math
How to convert mm to D
Power and focal length are reciprocals: diopters = 1 ÷ focal length in meters, so focal length in mm = 1000 ÷ diopters.
Example: 2 mm = 500 D.
Every unit
Your lens in every unit
Tables
mm to D conversion table
| mm | D |
|---|---|
| 50 mm | 20 D |
| 100 mm | 10 D |
| 167 mm | 5.98802 D |
| 250 mm | 4 D |
| 333 mm | 3.003 D |
| 400 mm | 2.5 D |
| 500 mm | 2 D |
| 667 mm | 1.49925 D |
| 1,000 mm | 1 D |
| 2,000 mm | 0.5 D |
| 4,000 mm | 0.25 D |
D to mm conversion table
| D | mm |
|---|---|
| 0.25 D | 4,000 mm |
| 0.5 D | 2,000 mm |
| 1 D | 1,000 mm |
| 1.5 D | 666.667 mm |
| 2 D | 500 mm |
| 2.5 D | 400 mm |
| 3 D | 333.333 mm |
| 4 D | 250 mm |
| 6 D | 166.667 mm |
| 10 D | 100 mm |
| 20 D | 50 mm |
Quick answers
Quick answers
- How many D is 1 mm?
- 1 mm is 1,000 D.
- How many D is 10 mm?
- 10 mm is 100 D.
- How many D is 2 mm?
- 2 mm is 500 D.
The units
About these units
Focal length in millimeters (mm)
How camera and microscope lenses are labeled.
Diopters (D)
One divided by the focal length in meters. Diopters simply add.
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