Bit of shameless plug here but also advice. Hope I can help you with your panic buying of bog roll or bleach these days.
It's strange how they don't consistently do unit pricing here. At Fusion (Park N Shop) they put in the unit pricing for stuff that's on sale but rarely if ever on regularly priced items. Shops are required by law to display unit pricing in many places in the world.
It's simple enough, you divide the cost by the size then you compare the cost / unit, and pick the cheapest. Easy peasy.
However, we import products from all over the world here, which means they use all sorts of different units.
It gets a bit hairy doing the conversions when it's like fluid ounces to mils and so on.
Anyway, here is the plug, a few years ago I wrote this app for Android that helps you calculate Unit Pricing and I was basically the only user but at least 1 other person liked it so I thought I'd spread the good word.
I had done an iOS version too but it hasn't been updated and I took it down. So for iPhone users, I just whipped up a quick web-app version so you all can use it too.
There are 2 versions for Android, one is free (ad supported) and the other is ad free for like $15 HKD.