3T fits like a small 2TWe bought these for under my son's snowsuit. I loved how snug fitting they were but found them to run small because of that, so we had to exchange for a size up. My son is 33lbs and mostly in a 3T, but we fit much better in a 4T. Even if they are a little long, it's fine since the ankles are fitted. Overall a great set of long Johns for the snow!I looked at the reviews & sized up but it was still small on him. It was extremely tight & I doubt it’ll last until the snow hits. He’s a 2T & I bought a 3TMy son is a big boy, but I got this for him when he was 8 months old and I got the 12 months size. He wore it once and even that one time it was pretty tight! After washing it, it shrunk a bit. So he wasn’t able to wear it again. Maybe it should be dried in the dryer. But still size upI ordered a 5T and it’s still too small for my 1 year old whose wearing 5T clothes. I recommend sizing up a size or two.Good productCute a little small order a size upI am giving it 2 stars because the sewing has poor quality. The material is nice, kept my 15 months baby warm in a really cold day in the mountains but the seam opened after the first day he wore the pants. He wears size 2T but I bought size 4T because of the reviews. But really runs too small.