Clark’s childs shoe sizes - how much to size up by?

[NemophilistRebel]

I’ve measured my sons feet at 146mm in length and he has a wide fit.

Based on the Clark’s shoe size guide how much would you size up by in ankle hiking type boots?
Half a size 0.5mm or a whole size 1cm?

I read somewhere that sizing is generous for clarks. I tend to get half a size bigger for my sons wide feet.