Ruler Now

Blog

How to measure your pupillary distance (PD) at home

2 min read

When you order glasses online you’re asked for your PD, the distance between the centers of your pupils in millimeters. It tells the lab where to put the optical center of each lens. It isn’t always on your prescription, but you can measure it yourself in a couple of minutes.

What you need

  • A ruler with millimeters. A printed one is easiest: our printable ruler works well.
  • A mirror, or better, a friend.

Measuring with a friend (most accurate)

  1. Sit facing each other at about arm’s length, at the same height.
  2. Look straight at a point in the distance over your friend’s shoulder, not at them.
  3. Your friend holds the ruler against your brow, lines up the 0 with the center of one pupil, and reads the number at the center of the other pupil.
  4. Repeat two or three times. The readings should agree within a millimeter.

Measuring in a mirror

  1. Stand about 20 cm (8 inches) from a mirror.
  2. Hold the ruler flat against your brow, just above your eyes.
  3. Close your right eye. Line up the 0 with the center of your left pupil.
  4. Without moving the ruler, close your left eye and open your right. Read the mark at the center of your right pupil.
  5. Do it three times and use the most common result.

Keep your head still and the ruler level. Tilting it by even a few degrees changes the reading.

What’s a normal PD?

For adults, PD is usually between 54 and 74 mm, with most people somewhere around 60–66 mm. Children’s PDs are smaller, roughly 43–58 mm. If your result is far outside these ranges, measure again.

Single PD and dual PD

The number above is a single PD. Some sites ask for a dual PD: the distance from the middle of your nose to each pupil separately, for example 31.5 / 32. To measure it, hold the ruler’s 0 on the center of your nose bridge instead and read each eye in turn. Faces are rarely perfectly symmetrical, so dual PD is more precise.

Distance PD and near PD

What you measured looking into the distance is your distance PD, used for everyday and driving glasses. For reading glasses your eyes turn inward slightly, and the near PD is usually about 3 mm smaller.

When to see an optician instead

A home measurement is fine for most single-vision glasses. For progressive or bifocal lenses, strong prescriptions, or children’s glasses, ask an optician to measure. They can do it in seconds, and with those lenses a small error matters more.