Diopters to focal length in inches
Type a value in D to get it in in instantly.
19.69in
That's about the same as reading glasses. That brings light to a focus about 500 mm away.
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 D to in
Power and focal length are reciprocals: diopters = 1 ÷ focal length in meters, so focal length in mm = 1000 ÷ diopters.
Example: 2 D = 19.685 in.
Every unit
Your lens in every unit
Tables
D to in conversion table
| D | in |
|---|---|
| 0.25 D | 157.48 in |
| 0.5 D | 78.7402 in |
| 1 D | 39.3701 in |
| 1.5 D | 26.2467 in |
| 2 D | 19.685 in |
| 2.5 D | 15.748 in |
| 3 D | 13.1234 in |
| 4 D | 9.84252 in |
| 6 D | 6.56168 in |
| 10 D | 3.93701 in |
| 20 D | 1.9685 in |
in to D conversion table
| in | D |
|---|---|
| 0.25 in | 157.48 D |
| 0.5 in | 78.7402 D |
| 1 in | 39.3701 D |
| 1.5 in | 26.2467 D |
| 2 in | 19.685 D |
| 2.5 in | 15.748 D |
| 3 in | 13.1234 D |
| 4 in | 9.84252 D |
| 6 in | 6.56168 D |
| 10 in | 3.93701 D |
| 20 in | 1.9685 D |
Quick answers
Quick answers
- How many in is 1 D?
- 1 D is 39.3701 in.
- How many in is 10 D?
- 10 D is 3.93701 in.
- How many in is 2 D?
- 2 D is 19.685 in.
The units
About these units
Diopters (D)
One divided by the focal length in meters. Diopters simply add.
Focal length in inches (in)
Used for telescopes and older optics.
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