The people I use set the basket on the scale and "O" the scale out then put your perch into that same basket and put it back on the scale. They have done this every time I have stopped there. Unfortunately I think you are guessing without having actual weight, but to really be sure just put an extra scale in your trunk and weigh your fish before taking them inside then you will know for sure. My bigger concern is how much fillets you really get back....with some cleaners I get 10-15% less returned fillets than thru my regular cleaner. They do charge a little more but have less waste and nicer fillets.