Drop rate

Drop Rate is the frequency at which a monster is expected to yield a certain item when killed by players. When calculating a drop rate, divide the number of times you have gotten the certain item, by the total number of that NPC that you have killed. For example:


 * Bones have a 100% drop rate from Chickens
 * Feathers have approximately a 75% drop rate from Chickens

A popular misconception is that you are guaranteed that item when you kill the NPC N number of times, where 1/N is the drop rate. You are never guaranteed anything, no matter how many of that monster you kill. For example:

If dust devils are expected to drop a Dragon Chainbody once out of 15000 kills, then the probability that you will get at least one drop in 15000 kills is:

1-(14999/15000)^15000

Which is approximately 63.21%. Similarly, we can solve for the number of Dust Devils you need to kill to have a 90% probability of getting one when you kill them:

1-(14999/15000)^(floor(X))>0.9

Which yields the answer 34538. Thus, we have shown that, while being counterintuitive, drop rates are not what they seem to be.