How to find my PD

What PD is

PD, or pupillary distance, is the distance between the centres of your pupils, measured in millimetres. It tells the lab where to place the optical centre of each lens so that you look through the exact point where the prescription is correct.

An adult PD usually sits between 56 and 72 mm. It does not change once you are fully grown, so once you have measured it you can reuse it for every pair.

We ask for it because it is not always written on a prescription, and the lab cannot guess it from the frame. A PD that is off by more than 2 mm can cause eye strain or a slight pulling feeling, so it is worth a minute to get it right.

Option 1: read it from your prescription

This is the most accurate method. Look for a box labelled PD, Pupillary Distance, or sometimes Dist. PD. It usually sits to the right of the sphere, cylinder and axis columns.

You may see it written in one of two ways:

• A single number, such as 64. This is your binocular PD. Enter it as it is.
• Two numbers, such as 32 / 31.5 or R 32 L 31.5. This is your monocular PD, one value per eye. Enter both; the order form has a field for each.

If two numbers appear with a slash and the second is much smaller, for example 64 / 61, the first is your distance PD and the second is your reading PD. Use the first one. Sunglasses and everyday glasses are made for distance.

If the PD box is empty, your optician measured it but did not write it down. They are usually happy to give it to you by phone or email. In some countries you are entitled to it as part of your prescription.

Option 2: measure it yourself with a ruler

You need a ruler marked in millimetres, a mirror, and good light. It takes about two minutes.

1. Stand about 20 cm from the mirror, face straight on, and look at your own eyes.
2. Hold the ruler flat against your brow, just above your eyes, with the millimetre scale facing the mirror.
3. Close your right eye. With your left eye open, line up the 0 mark with the centre of your left pupil.
4. Keep the ruler still. Open your right eye and close your left.
5. Read the mark that sits over the centre of your right pupil. That number is your PD.
6. Repeat two or three times. If the readings differ by a millimetre, use the middle one.

Tips that make it more accurate:

• Look straight at the mirror, not at the ruler. Focusing on the ruler makes your eyes converge and reads 2 to 3 mm too low.
• Keep your head level and do not tilt the ruler.
• Take your glasses off if the lenses distort the reflection.

If you want monocular values, measure from the centre of your nose bridge to the centre of each pupil instead, one eye at a time. The two numbers should add up to your binocular PD.

Option 3: have someone measure it for you

A second person removes the mirror and the convergence problem, so this is slightly more accurate than measuring alone.

1. Sit facing each other at roughly arm's length, eyes level.
2. Look at a fixed point behind them, such as a picture on the far wall. Keep looking there for the whole measurement.
3. They hold the ruler across your brow, just above your eyes, and close their right eye.
4. With their left eye, they line up the 0 mark with the centre of your right pupil.
5. Keeping the ruler still, they close their left eye and open their right, and read the mark over the centre of your left pupil.
6. Repeat once or twice and take the average.

If you prefer, any optician will measure it in under a minute. Most do it for free, even if you did not buy your glasses there.

What to enter on the order form

Enter your PD in millimetres, in 0.5 mm steps.

Field	Typical range	Enter this
Binocular PD (single number)	56 to 72 mm	The one number from your prescription or ruler
Monocular PD, right	28 to 36 mm	Right-eye value only, if you have two numbers
Monocular PD, left	28 to 36 mm	Left-eye value only, if you have two numbers

If you have a single number, leave the monocular fields empty. If you have two numbers, leave the binocular field empty. Do not enter both.

We currently fill prescriptions with a PD between 56 and 72 mm. If yours falls outside that range, contact us before ordering and we will check whether the frame can be made for you.

Common questions

Does it need to be exact? Within 1 mm is fine for single vision lenses. The difference between 63 and 64 is not something you will notice. Being 3 mm or more out is worth correcting.

My prescription has a different PD than I measured. Which do I use? Use the one on the prescription. An optician's measurement is more reliable than a ruler in a mirror.

My two monocular values are not equal. Is that normal? Yes. Most faces are slightly asymmetric, and a difference of 1 to 2 mm between eyes is common. Enter them as they are.

Should I use my distance PD or my reading PD? Distance. All of our lenses are single vision for distance, which includes sunglasses.

I only have a PD from a pair bought years ago. Can I reuse it? Yes. Adult PD does not change. The only exception is if that pair was made for reading, in which case the PD will be a few millimetres too narrow.

I can't find my PD and can't measure it. What now? Ask your optician, or email us a straight-on photo of your face with a standard bank card held flat against your forehead, and we will measure it for you using the card's known width.