There are lots of digital tools and apps out there that can scan and measure it. Ideally, you need your duel pupillary distance measurements (also called monocular centration distance) - basically a right and left measurement, measured from the centre of your nose.

ZEISSlensthicknesscalculator

- Your Interpupillary Distance (PD) is the distance between the centre of each of your pupils. The average PD for men is 64, and for women it's 61.

Your Pupillary Distance is a key variable in estimating thickness, and is the distance between the centre of your right and left pupils. You can read more about this in our article on lens thickness.

- The frame eye size and bridge, you should be able to find on the glasses description and is usually in this format: 46-22-145. These are usually found written on the inside of every pair of glasses too.

zeiss real-timelensthicknesscalculatorand visualizer

You'll need your prescription including your pupillary distance (PD), and the measurements of the glasses. For the calc mentioned above, these are some of the details that you'll need to fill in;

If you're buying your frames in-store, ask the staff to support you on predicting lens thickness. If they say it's not possible, push them or ask them to find out more information. If you're being helped by a sales staff member, then ask them to bring out a big dog who's more trained, liked the optician. Some stores might even have the staff that make and fit the lenses who you can talk to.

Twolens calculator

Keep in mind that this is not a full proof estimation, because of the lens shape and how it will be cut out to fit your glasses.

Lensthickness chart

We've dropped in some examples below to demonstrate lens thickness in a couple of our frames, which also shows how PD can impact the end results.

- Lens material is the thinning option you've been recommended, or that you usually get. The thinnest option featured would be 1.74 for plastic lenses.

We're really hoping to add our own calculator in the future, and simulate some example lenses in our frames to take away the guess work. Take a look at our range of glasses designed specifically for thick minus lenses here or head over to our socials for examples of frames with fitted lenses.

It's possible to work out an estimate of how thick your lenses will end up being in each pair of frames you're thinking of getting, and for each eye. You can use an online calculator like this one.