How to weigh ur baby

Ok so I’m bf she’s currently 5months old and always paranoid of her gaining weight. She was born 9llbs and I took her at 5months to recheck her weight she was 15lbs&10oz ishhh close to 16.

I only have a bathroom scale at home and I’ve seen to weigh urself then weigh urself w the baby subtract etc. I get 17pounds. And when I weigh her laying down on it I get 16.5lbs.

At her 4m she was 15lbs 5oz so I thought it was weird she stayed close to the weight for 5months when she was gaining over 1-2lbs per month. So which weight do I trust lol!

I really want a baby scale but I can’t find any close to me off martketplace and buying one seems really expensive to me $60+.

I called the hospital bc I read online I can rent a baby scale. If anyone has what was the price etc? Idk I need advice !