The PD Journal
Binocular to Monocular PD: How to Split or Combine Your PD
Last updated: October 2026 | Reading time: 6 minutes
Short answer: to turn a single (binocular) PD into two monocular numbers, divide it by two: 64 becomes 32 and 32. To go the other way, add the two numbers: 31.5 + 32.5 = 64. Dividing by two is only an approximation, because most faces are not perfectly symmetric.
Definitions in one minute
- Binocular PD (single PD): one number, pupil to pupil. Example: 64.
- Monocular PD (dual PD): two numbers, each from the centre of the nose bridge to one pupil. Example: 31.5 / 32.5. The first number is the right eye, the second the left eye.
For the full distinction, see monocular vs binocular PD and single PD vs dual PD.
Combining: monocular to binocular
Add the two numbers.
| Right | Left | Binocular |
|---|---|---|
| 31.0 | 31.0 | 62.0 |
| 31.5 | 32.5 | 64.0 |
| 32.0 | 33.5 | 65.5 |
| 30.5 | 32.0 | 62.5 |
Splitting: binocular to monocular
Halve it for a rough guide.
| Binocular | Estimated each eye |
|---|---|
| 58 | 29.0 |
| 60 | 30.0 |
| 62 | 31.0 |
| 64 | 32.0 |
| 66 | 33.0 |
| 68 | 34.0 |
A small difference between the eyes is normal, often a millimetre or so. A larger difference matters more, especially for strong prescriptions and progressive lenses.
When splitting is not good enough
- You use progressive lenses.
- Your prescription is strong.
- You know your face is asymmetric.
In these cases, use measured monocular values. Our PD tool reports left and right values measured from the centre of your nose bridge, and the two values always add up to the binocular PD it displays.
Which number do online shops want?
Many online stores accept a single PD and some ask for two. Enter what the form asks for. If it has a single field and you have two numbers, enter their sum. If you only have a single number and the form asks for two, halving is common practice for simple glasses.
Common mistakes
- Entering one monocular number as if it were the binocular PD (for example, 32 instead of 64).
- Swapping right and left.
- Mixing near and distance values. See near PD vs distance PD.
Related
How to read PD on a glasses prescription · Buying glasses online: the PD guide