I feel silly for this, but I've never weighed a chicken. Do I need a specific scale, and how do I do it?
Stand on a scale, see how much you weigh. Have someone hand you the chicken, see how much you + chicken weigh.
Subtract your weight from the combined weight. What's left is the chicken's weight.
(If no-one is available to hand you the chicken, you can do it in the other order: weigh yourself with the chicken, let him go, weigh yourself without him. Same math to get the chicken's weight.)
Question is what to do? Or not do?
Do you have hens, or even pullets, that he can live with?
He may need practice in how to be a chicken! Because we all know he isn't a person, but he may not be so sure.