Trial and error, every brand fits differently and every baby is different. My chucky butt grew out of stuff so fast the first year.

I’d usually go a size up knowing with multiple washings that the clothes will shrink. You’ll learn as you go that some brands run true to size and the others could run smaller. It’s a lot of trial and error and look at an item and asking yourself is this too big or too small. It’s also better to have clothes a lil larger so they get more use out of them. Clothes that are too small theirs nothing u can do about it and it’s a waste.

trial & error. my son is only 10 months but can still fit into some 3-6 month shirts (he’s a skinny minnie) but has to wear 12 or 18 month pants. just gotta see what works!

Nope. Just like our clothing, there are even differences between different items of the same brand. I’d say try visually measuring and grouping things together. My daughter definitely missed out on some cute outfits because I had separated everything by actual tag size.

Unfortunately, no. Except that Gerber always ran small and then shrank for me. Disney tends to run small, as do a lot of the character clothing. But I had a pack of three pants once, 6 month size I think, and all three were different. All the same brand and labeled the same, though.