How-to · Updated October 2, 2026
How do you calculate near PD from distance PD?
Direct answer
Near PD = distance PD × L ÷ (L + 27 mm). L is the reading distance. At 40 cm the factor is 0.937, so a 64 mm distance PD becomes 60 mm. Subtracting 3 mm instead gives 61 mm.
Reading PD and computer PD
| Distance PD | Reading, 40 cm | Computer, 60 cm |
|---|---|---|
| 58 mm | 54.3 mm | 55.5 mm |
| 60 mm | 56.2 mm | 57.4 mm |
| 62 mm | 58.1 mm | 59.3 mm |
| 63 mm | 59 mm | 60.3 mm |
| 64 mm | 60 mm | 61.2 mm |
| 66 mm | 61.8 mm | 63.2 mm |
| 68 mm | 63.7 mm | 65.1 mm |
| 70 mm | 65.6 mm | 67 mm |
The 27 mm figure is the conventional spectacle-plane to centre-of-rotation distance from Jalie. A closer book makes the near PD smaller: 64 mm at 25 cm is 57.8 mm.
Which number to order
- Reading glasses only: the near PD. For 64 mm at 40 cm, that is 60 mm, sometimes written 64/60.
- Distance glasses, sunglasses, and progressives: the distance PD. The lab calculates the near inset.
- Computer glasses: the intermediate PD. For 64 mm at 60 cm, that is 61.2 mm.
- Dual PD 32/30: each eye insets on its own. At 40 cm the near pair is 30/28.1.
Limits
- This is a centration estimate, not a prescription and not a measured near PD from a pupilometer.
- A 1 mm error matters more in a strong progressive than in a low-power single-vision lens. An optician's measurement is the one to order.
- Two close numbers (31/32) are a dual distance PD. Two numbers several millimetres apart (62/58) are distance and near.
Use the calculator
Where 64 mm sits in the population: what is the average pupillary distance? Enter your own distance in the PD calculator.