Question about Supermagnete Neodymium magnetic hook

I've tried it with a pack of coke, it doesn't work with 4kg, it holds my use is for a big bunch of keys, it holds very well. I've tried it with a 4 kg pack of coke, it doesn't work with 4 kg, but it works well. If I am not mistaken, the strength of the magnet is in relation to its surface area. You can find some advice on the internet by typing in "type of magnet, how to choose".