Check the scale first. A 3% printing error changes a 64 mm PD by about 2 mm, which is enough to matter for strong prescriptions. Print at 100% and check the scale bars, or the bank-card outline, before measuring.
How to measure your PD with a mirror
- Cut out one of the rulers. Stand about 20 cm (8 in) in front of a mirror, in good light.
- Hold the ruler flat against your face, just under your eyes, with the millimetre marks at the top.
- Close your right eye and look straight ahead. Line up the 0 mark with the centre of your left pupil.
- Close your left eye and open your right. Without moving the ruler, read the mark under the centre of your right pupil. That number is your PD.
- Repeat three times and use the average.
With a helper (more accurate)
Ask someone to sit at your eye level, about an arm's length away. Look at a point far behind them, not at their face. They hold the ruler under your eyes, line up 0 with your right pupil (their left), and read the mark at the centre of your left pupil. Looking into the distance keeps your eyes straight, which gives your distance PD, the number most glasses use.
Single PD, dual PD and near PD
| Term | What it means |
|---|---|
| Single PD | Pupil to pupil, for example 63 mm. Most adults fall between 54 and 74 mm. |
| Dual (monocular) PD | Each eye to the centre of the nose bridge, for example 31.5 / 31.5. It is often needed for progressive lenses. |
| Near PD | For reading glasses only. It is usually about 3 mm less than your distance PD. |
For strong, high-index or progressive prescriptions, ask an optician to measure your PD. A printed ruler is fine for most single-vision glasses.
Frequently asked questions
What is a normal PD?
Most adults are between 54 and 74 mm, and the average is about 63 mm. Children are usually between 41 and 55 mm.
Can I measure PD myself accurately?
Yes, to within about 1 mm, if the ruler printed at 100% scale and you repeat the measurement a few times. A helper makes it easier.
Is PD on my prescription?
Often not. Many opticians measure it but do not write it down. You can ask your optician for it, or measure it with this ruler.
My printout is slightly too small. What went wrong?
Almost always the print window was set to "Fit to page", "Fit to printable area" or "Shrink oversized pages", which shrinks the page by 3–6%. Print again with Scale 100% or Actual size. See how to print at actual size for every browser.
Last reviewed 2026-10-07.