When do you know when it's time to go from a toddler bed to a twin size bed?

my husband and i disagree on whether it is time for our 3 year old to have a big bed yet. he is 3 years old, and has had his toddler bed since he turned 2 years old.. he weighs about 40 lbs but he has long legs. at night sometimes when i go in to check on him he is literally hanging off of the bed. his legs will be in hanging off the side in the floor, i have even seen him hanging off with his head and shoulders and chest down on a pillow in the floor and his legs and feet on the bed. i think he is just too big for it, but my husband insists that he is just fine, that his toddler bed should last him until he is at least 6 years old??? seriously? could you imagine? lol...a few weeks ago the children and i went to visit my parents and the my son and i shared a full size bed, and i would put him to bed before i would go, and when i would go in to bed, i would have to move him over because he made himself comfy by getting right in the middle and spreading his legs and arms out wide. he loved it. and now that we are home, he lasts in his bed until about 2-3 a.m. and then has been coming to get in bed with me when my husband gets up to go to work.. he loves the extra space and i think he needs it.. how do i get my hubby to understand that the poor little fella needs more space? i think he's just being cheap and not wanting to buy a new bed, or he just hates the fact that our little boy is growing so fast and i can sympathize but, he is a growing boy and needs to be able to sleep comfortably. i'd like to see my hubby cram his body in to a tiny bed and sleep all night to see how it feels.. so, do you think it's time for a bigger bed? or is he right, should we wait?