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Printable PD ruler

A millimeter ruler sized for measuring pupillary distance, with a calibration bar so you can tell at a glance whether your printer scaled the page. Print it, cut the strip out, and measure in a mirror — or skip the paper and let an iPhone read the distance directly.

Set scaling to 100% / “Actual size”, then check the bar below.

Calibration bar — this is exactly 100 mm

Measure it after printing. A standard bank card is 85.6 mm wide and should fall 14.4 mm short of the end. If it does not, reprint at 100% scale.

PD ruler — 150 mm

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Numbers are centimeters; the small marks are millimeters. Cut along the strip and keep the marked edge straight.

How to measure your PD with the printed ruler

1. Print at 100% scale and confirm the calibration bar measures 100 mm.
2. Cut out the strip so the marked edge is clean and straight.
3. Stand about 20 cm from a mirror and hold the strip flat against your brow, marks down.
4. Close your right eye. Slide the strip so zero sits over the center of your left pupil.
5. Hold it still, close your left eye, open your right, and read the mark over your right pupil.
6. Repeat three times and average. If your readings spread by more than a few millimeters, slow down and redo them.

One caveat worth knowing before you order lenses: your reflection sits about twice the mirror distance away, so a mirror reading behaves more like your near PD and tends to come out a couple of millimeters low. The full guide to measuring your PD at home covers that, the friend method, and what the numbers mean. To convert the result into near PD or per-eye values, use the PD calculator.

Or skip the ruler

Paper works, but it fights physics: the moment your line of sight is not perfectly perpendicular to the marks, parallax pushes the reading too wide, and self-measurement in a mirror repeats to only about ±4 mm. An iPhone with a TrueDepth front camera measures the distance between your pupils in three dimensions instead, and returns far PD, near PD and both monocular values in a single pass. The Pupillary Distance app does exactly that, on device.

Common questions

How do I print a PD ruler at the correct size?

Print at 100% scale — in the print dialog choose "Actual size" or set scaling to 100%, and turn off "fit to page". Then check the calibration bar on the printout: it is exactly 100 mm, so if a ruler or a bank card says otherwise, your printer scaled the page and the measurement will be wrong by the same proportion.

How do I use a printed PD ruler?

Hold the printed strip flat against your brow with the millimeter edge down, stand about 20 cm from a mirror, close your right eye and line the zero up with the center of your left pupil, then — without moving the ruler — close your left eye and read the mark over your right pupil. Keep your head straight and the ruler level, and take three readings.

How accurate is a paper PD ruler?

Less accurate than most people expect. Measuring your own PD in a mirror repeats to roughly ±4 mm between attempts, against about ±1 mm for a trained examiner using a proper PD rule, and the mirror method reads low because your reflection sits about twice the mirror distance away. Average several readings and treat the result as an estimate.

Can I use a bank card instead of a printed ruler?

A card is useful for checking your print scale, not for measuring. Every ID-1 card is 85.6 mm wide by 53.98 mm tall, so holding one against the calibration bar tells you immediately whether the page printed at true size. It has no millimeter markings, so it cannot give you a PD on its own.

Is there a way to skip the ruler entirely?

Yes. An iPhone with a TrueDepth front camera measures the distance between your pupils directly, with no paper, no mirror and no second person, and returns far, near and left/right monocular PD in one pass. That removes the parallax that makes ruler readings come out too wide.

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