A Southwest Airlines passenger is allowed to check two pieces of luggage weighing up to 50lbs each for free. It’s a generous allowance. But if one bag weighs 55 lbs and the other weighs 45 lbs, you’ll get charged $(removed) for the heavier bag.
Other airlines have similar pricing arrangement. I bought this illuminated $(removed) luggage scale last year to weigh checked and carry-on luggage and it’s really easy to use — much easier than standing on a bathroom scale while holding the luggage and subtracting my weight. You just loop the strap around the luggage handle and lift it. It has a built in digital thermometer (because why?). You can switch between pounds and kilograms, too.