Otteroo works in most standard-sized tubs! You want the water deep enough so that your baby is mostly floating, instead of sitting on the bottom of the tub (while wearing Otteroo). If your baby is bigger, or particularly active/strong, it is very important that there is enough water so that when they kick off the bottom, they can’t push off the tub with too much force. Doing so could cause your baby to tip over, and repetitive forceful pushing against the tub wall can wear down the floatie. You can prevent too forceful a kick by making sure that your baby’s feet are only able to skim the floor when their legs are straight, or take your Otteroo to a pool where there is more room for them to use their arms and legs freely!