The weight of a 750 gram cardboard spool is 152 gram.
More about spool weights and dimensions can be found here:
https://colorfabb.com/spool-dimensions
Other spool weights:
Plastic 750gr spool without the filament is 255gr.
Cardboard 750gr spool without the filament is 152gr.
Plastic 1000gr (1kg) spool without the filament is 226gr.
Plastic 2200gr (2,2kg) spool without the filament is 600gr.
Plastic 4500gr (4,5kg) spool without the filament is 700gr.
Plastic 8000gr (8kg) spool without the filament is 1050gr.