How to Measure Your PD at Home (Step-by-Step Guide)
Measuring your pupillary distance (PD) accurately is crucial for ordering prescription glasses online. Your PD determines where your pupils align with the optical centre of your lenses — get it wrong, and you'll experience eye strain, headaches, or blurred vision.
Photo by Sedanur Kunuk / Pexels
What Is Pupillary Distance and Why It Matters
Pupillary distance is the measurement in millimetres between the centres of your pupils. Most adults have a PD between 54-74mm, with the average being around 63mm. This measurement ensures your prescription lenses are positioned correctly in front of your eyes.
Critical fact most people miss: Your PD can vary by 1-2mm depending on whether you're looking at something far away (distance PD) or reading up close (near PD). For single vision distance glasses, you'll use your distance PD. For progressive lenses, your optician may use a slightly different measurement for the near portion.
Method 1: Online Try-On with Automatic PD Measurement
The easiest and most accurate way is to use Lensdy's free Online Try-On tool at lensdy.com. This innovative feature uses your webcam or phone camera to measure your PD automatically while letting you virtually try on frames before you buy. The technology analyses the distance between your pupils in real-time, giving you an instant, accurate measurement.
Simply visit any frame page, click "Try On", allow camera access, and the system will detect and display your PD measurement. This method eliminates human error and works particularly well for customers in Oslo, Bergen, Stavanger, and Trondheim who want professional accuracy without visiting an optician.
Method 2: The Ruler Method (Most Common DIY Approach)
You'll need a millimetre ruler and a mirror. Here's the precise technique:
- Position yourself: Stand 20cm from a mirror in good lighting
- Hold the ruler: Place it horizontally against your brow, with the zero mark aligned above your right pupil
- Look straight ahead: Focus on your own eyes in the mirror, not the ruler
- Read the measurement: Note where your left pupil centre aligns on the ruler
- Repeat 3 times: Take three measurements and use the average
Pro tip from opticians: If your measurements vary by more than 2mm between attempts, you're likely moving your head or eyes. Stay completely still and focus on a fixed point behind your reflection in the mirror.
Method 3: The Credit Card Method (More Accurate Reference)
Standard credit cards are exactly 85.6mm wide, making them excellent measuring references:
- Hold a credit card horizontally below your eyes
- Mark the card with a pen where each pupil centre aligns
- Measure the distance between marks with a ruler
- This method reduces parallax error common with the ruler-only approach
Method 4: The Helper Method (Most Accurate DIY Option)
Having someone else measure eliminates the mirror parallax issue:
- Sit facing your helper at eye level
- Look at a fixed point 6 metres away (not at your helper)
- Helper holds ruler across your brow and measures pupil-to-pupil distance
- Take multiple measurements for consistency
Common PD Measurement Mistakes to Avoid
| Mistake | Why It Happens | How to Fix It |
|---|---|---|
| Measuring to iris edge instead of pupil centre | Poor lighting or unclear pupil boundaries | Use bright, even lighting and focus on the dark pupil centre |
| Head tilting during measurement | Natural tendency when concentrating | Keep chin level, shoulders square |
| Using near vision instead of distance | Looking at ruler or helper's face | Focus on distant object throughout measurement |
| Single measurement only | Assuming first attempt is correct | Take 3-5 measurements, discard outliers |
Professional PD vs DIY: When Each Is Appropriate
For standard single vision prescriptions with low to moderate power, home measurement works excellently. However, consider professional measurement for:
- Progressive or varifocal lenses (require near PD and fitting height)
- High prescriptions over ±4.00 dioptres
- Prism corrections or significant astigmatism
- Bifocal or trifocal lenses
Ordering Prescription Glasses Online with Your PD
Once you have your accurate PD measurement, you're ready to order prescription glasses online. Lensdy offers over 200 frame styles with prescription lenses starting from just £29, shipping free to Norway within 5-10 business days from our London headquarters at 128 City Road.
Popular frame choices for Norwegian customers include the elegant SkyAura acetate frames, the lightweight Vertex titanium collection, and the versatile Rosélia memory metal frames that flex without breaking.
For those wanting both prescription glasses and sunglasses, consider the Pike Pink magnetic clip-on system, which transforms your prescription glasses into sunglasses instantly.
Frequently Asked Questions
What if my PD measurement is between two numbers?
Always round to the nearest whole millimetre. If you consistently measure 62.5mm, use 63mm. The 0.5mm difference won't significantly impact your vision with standard prescriptions.
Do I need different PD measurements for distance and reading glasses?
For single vision glasses (either distance or reading only), use your distance PD. For progressive lenses, your near PD is typically 2-3mm smaller than your distance PD, but most online retailers use distance PD for all calculations.
Can PD change over time?
Adult PD remains stable after age 20. Children's PD increases as they grow, but adult measurements shouldn't vary more than 1mm over decades. If you measure significantly different PD than previous glasses, double-check your measurement technique.
Is it safe to order glasses online with self-measured PD?
Yes, for standard prescriptions. Online retailers like Lensdy use the same lens manufacturing processes as high-street opticians. With accurate PD measurement and current prescription, your online glasses will be identical to those made in-store.
Ready to order your new glasses? Browse Lensdy's complete collection of prescription frames, progressive lenses, and designer styles at lensdy.com — with free shipping across Norway and our Online Try-On tool, you'll find the perfect frames with confidence.