Big kid bed?

Just curious if anyone has moved their toddler out of their crib yet. We got a mini crib (first time mom and had no idea there was more than one size crib!) at her baby shower and she still fits it...barely. We have a twin bed on standby for when she’s ready, but I that it will be a big transition and I have no idea when is considered an appropriate time to move her out of her crib. I guess if you have moved: how did you know your child was ready? Or when do you plan to move your child up to a big kid bed?