How can I target the current selected quantity on a product page?

Hi all,

Can anyone point me in the right direction on how to target the current selected quantity on a product page?

I’m trying to use a metafield to adjust the step count only when the current value equals the metafield number, once it does it should increase by the amount of the metafield.

i.e if the metafield = 10 then start value would be one and it would increase by 1 until it reaches 10, at this point it should increase by multiples of 10.

I’ve got the start, value and step to work off the metafield but just stuck on this last part on how to query the current selected qty.

I’m not looking to use an app so no need to suggest any apps for this.

Thanks,
Matt.