Baby clothes sizing is all over the place across UK brands — anyone else dealing with this?

My son is about to turn 4 months and growing fast (already on the longer/taller side for his age), so I’ve been buying across a few different high street and supermarket brands and the difference in fit for the “same” size label has been honestly baffling.

A few examples from my own experience, all washed the same gentle/cold cycle so I don’t think it’s shrinkage:

•	Asda (Winnie the Pooh range) 3-6 months — so tight, barely fit him  
•	Other Asda pieces — fit fine now but definitely on the smaller side  
•	Primark 3-6 months — noticeably roomier, even after washing  
•	H&M 4-6 months — also runs generous  
•	Sainsbury’s (Tu) — reliable, good sizing  
•	John Lewis 3-6 months — small despite the label  
•	Uniqlo — true to size, no surprises

Since I keep the wash consistent, it feels like it’s really down to how each brand cuts their patterns rather than anything happening in the machine.

Has anyone else found this? Which brands have you found run generous or true to size, especially for a longer/fast-growing baby? Also curious if anyone’s had better luck going by weight/height guide instead of the age label. Trying to stop guessing wrong every time I order!