Medium would be too large, IMO, considering my 1780g girl eats one small rat. But I'm no expert (at least not compared to others here), so don't quote me on that! They say the "rule" is about 10-15% of the snake's body weight for prey, so I guess a rat weighing approx. 55-60g would be appropriate... I brought my digital scale to the pet store yesterday, which really helped to gauge the right sized mice/rats for my BPs. Getting them to stand still for weighing was a challenge though, LOL.