Free online PD ruler

A millimeter ruler on your screen, calibrated with any standard bank card. No printer needed (there is also a printable PDF version). For a faster, hands-free measurement, PDgo measures your PD automatically in 10 seconds.

Step 1 · Calibrate with a bank card

Hold any standard card (credit, debit, ID - they are all 85.60 mm wide) against the box below, then drag the slider until the box is exactly as wide as your card.

match card width

Step 2 · Measure in a mirror

  1. Face a mirror at about 20 cm, or ask a friend to read for you.
  2. Rest this ruler flat under your eyes, against your brow.
  3. Close your right eye. Align the 0 mark with the center of your left pupil.
  4. Close your left eye. The mark at the center of your right pupil is your PD.

Typical adult PD is 54–74 mm. If you get a value far outside that, re-check the calibration.

Want it done for you? The mirror method takes practice and is easy to misread by a millimeter or two. PDgo uses your iPhone's TrueDepth 3D camera to measure automatically - total and per-eye PD with a confidence rating, in about 10 seconds. Get PDgo on the App Store →