Cows weigh from 300 to 600 pounds full grown. They can weigh up to 800 lbs when pregnant. Each breed has it's ideal weight when full grown.
Most bulls weight anywhere from 600 up to 1400 lbs. The Charolet bull can weigh up to 2400 lbs. Cattle weight depends a lot on the breed of cow, the diet, and stressors in the herd such as food supply, water supply, and grazing area.