Why worry about weight?
Airlines are checking that each individual bag does not exceed 50 lbs. which can happen very easily.
Use a floor scale to weigh yourself without your bag, then with your packed bag in hand; subtract the two weights to find the weight of the bag. There are also luggage scales available for direct weighing.
Reducing the weight of your bags by several pounds less than 50 affords you some allowance for anything you may pick up on your trip.