How can I use RegEx to differentiate between screen resolutions?

Question

I'm trying to create a RegEx expression that will match a numeric range from 0 to 600 so I can easily differentiate between a small mobile device and tablets/desktops. I'm using Qualtrics' survey software to do the rest - all I need is the RegEx expression.

However, I'm not 100% sure how Qualtrics takes in the data. I believe it takes it in the following format:

360x640
320x568
320x480
1920x1080
360x640
1280x800
320x568
1920x1080
360x640
1280x800
1920x1080
480x800
320x480
1280x800
1366x768
320x568
1280x800

Where I'm testing the FIRST number, e.g. the number before the 'x' character.

Here's some RegEx I've tried that did not work:

([0-9]{1,2}|[1-4][0-9]{2}|600)*x

That code recognizes numbers before the 'x', but it doesn't stop at 600 - it recognizes all numbers before the 'x' (e.g. from 000 to 9999).

How do I get the range I want? Please and thank you!

Note: I've tried using the RegEx number range generator here, but it doesn't work for what I want to accomplish.

Answer 1

I don't believe there are width lower than 100, so you can use this pattern:

^([1-5][0-9]{2}|600)x