What is the 95th percentile billing?

95th percentile billing is for higher-bandwidth customers, and reflects the way that we get charged for bandwidth. Rather than charge for total traffic, we get charged a per-mega*bit* rate (Mbit/s). This rate is calculated by taking 5-minute transfer rate readings throughout the month, then knocking off the top 5% of readings (i.e. hopefully all the spikes) and charging for the next highest rate on the list.

1Mb/s at a constant rate is 320GB, but you can still get charged for 1Mbit/s while transferring a lot less. As an extreme example: if you transferred 1Mbit/s for only 2 days in a month, only 25GB or so, then nothing for the rest it would still go over 5% of the month and thus incur a high charge relative to the total traffic.

Example graph

The graph below shows one of our customer’s transfer graphs for a particular month. It shows a 95th percentile transfer rate of 306Kbit/s (kilobits per second):

As you can see, the customer’s transfer rate actually peaked at nearly 800Kbit/s at one point in the month, but this is disregarded for charging purposes as it falls outside of the 95th percentile, i.e. these transfers were in the peak 5% of the month, and are not chargeable.

The total data transferred is the area under the green graph, which amounts to 47.2GB in this case. There is no way to convert between Megabits and Gigabytes when talking in terms of 95th percentile, because it can vary. e.g. if you transferred 100Mbit/s solidly for 2 days in a month and 1Mbit/s for the rest of the time, the 95th percentile would be the full 100Mbit/s because it exceeded 5% of the charging period. However if you transfer 100Mbit/s solidly for 1 day in a month, and only 1Mb the rest of the time, the 95th percentile would be 1Mbit/s (1% of the previous cost) despite using only half the data.