Answer:
If you're talking about the animals then:
Bats weigh from as little as 0.07 ounces up to 3.3 pounds. (2 g to 1.5kg) There are nearly 1,000 different bat species of varying sizes. The smallest bat species, the bumblebee bat, has an average wingspan of only 6 inches long and weighs less than a penny at 0.07 ounces. The largest bat, the flying fox, can have a wingspan as long as 6 or more feet and weigh more than 3 pounds.
If you're talking about the baseball bats then:
By regulation, baseball bats may weigh no more than 2.75 inches (7.0 cm) in diameter at the thickest part and no more than 42 inches (1.067 m) in length. Although historically bats approaching 3 pounds (1.4 kg) were swung, today bats of 33 ounces (0.94 kg) are common, topping out at 34 ounces (0.96 kg) to 36 ounces (1.0 kg).