Coming from very similar sports - softball comes from baseball - baseballs and softballs have and equally similar composition, with core, lines and lining, but with different densities (higher in the baseball), and, most importantly, different measurements.
If the baseball has a circumference between 22 and 23 centimetres, and weighs around 145 grams, more or less, the softball is about 30 centimetres in circumference and between 178 and 194 grams.