95th Percentile Calculator

Turn monthly transfer volume into the Mbps a carrier bills on, estimate your 95th percentile and see when a flat-rate port would cost less.

Inputs

Start from

Monthly volume (GB or TB) Average rate (Mbps)

Work one direction at a time. Many providers bill on whichever direction has the higher 95th percentile, which is not always the one with more volume, so run inbound and outbound separately and compare.

Data transferred in the month

Decimal units (1 TB = 1,000 GB).

Billing month

Bills often cover a calendar month; the average month is 365.25 ÷ 12 days.

Peak-to-average ratio (95th percentile ÷ average)

The default 2 is a placeholder, not a typical value. Steady traffic sits close to 1; spiky traffic runs higher. Divide a past month's billed 95th percentile by its average to get yours.

Optional: burstable pricing

Enter all three to estimate the bill.

Commit (Mbps)

Commit price ($ per Mbps)

Burst price ($ per Mbps)

Result

Enter the data transferred in the month to see the average rate.

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How the calculation works

Volume to average rate. One gigabyte (decimal, 10⁹ bytes) is 8,000 megabits, so:

average Mbps = GB × 8,000 ÷ seconds in the month
GB a month = average Mbps × seconds in the month ÷ 8,000

The month length matters by about 10% between February and a 31-day month, so it is an input: 28, 29, 30 or 31 days, or the 30.44-day average (365.25 ÷ 12). The default is 30 days, 2,592,000 seconds.

Estimated 95th percentile. Burstable (95/5) billing works from samples of the port’s traffic rate, usually taken every 5 minutes. At the end of the month the samples are sorted, the top 5% are discarded and the bill uses the highest remaining sample. Monthly volume alone cannot reproduce that, so the calculator multiplies the average by a ratio you set: estimated 95th = average Mbps × (95th ÷ average). The default ratio of 2 is a placeholder. Take your own from a past bill or usage graph: the billed 95th percentile divided by that month’s average rate.

Burstable bill (optional). With a commit and prices per Mbps:

commit charge = commit Mbps × commit price
burst charge = (95th − commit) × burst price, when the 95th is above the commit
bill = commit charge + burst charge

Any flat-rate or unmetered offer below that bill costs less for this traffic. Contract terms vary, for example in how usage above the commit is priced, how the 95th is rounded and whether inbound and outbound are measured separately, so check the billing definition before you compare.

Worked example

A colocation customer sends 100 TB a month outbound, the direction its provider’s samples show as the higher one, over a 30-day month (2,592,000 seconds):

average rate = 100,000 GB × 8,000 ÷ 2,592,000 = 308.64 Mbps
with a peak-to-average ratio of 2, the estimated 95th percentile is 617.28 Mbps

Illustrative prices, not market rates: a 500 Mbps commit at $1.00 per Mbps and burst at $1.50 per Mbps:

commit charge = 500 × $1.00 = $500.00
burst = 617.28 − 500 = 117.28 Mbps × $1.50 = $175.93
estimated bill = $675.93 a month, about $1.10 per Mbps of 95th percentile

A flat-rate port offered below $675.93 a month would cost less for this traffic, as long as the port is large enough to carry the peaks.

Going the other way, a steady average of 100 Mbps for a 30-day month moves 100 × 2,592,000 ÷ 8,000 = 32,400 GB, or 32.4 TB.

Frequently Asked Questions

How many GB a month is 1 Mbps?

A steady 1 Mbps for a 30-day month moves 324 GB: 1 Mbps × 2,592,000 seconds ÷ 8,000 megabits per GB. For a 31-day month it is 334.8 GB, and for the 30.44-day average month 328.7 GB. Traffic is rarely steady, so the same volume usually means a higher 95th percentile.

How is the 95th percentile calculated?

The provider samples the port's traffic rate every 5 minutes for the month, about 8,640 samples in 30 days. It sorts the samples, discards the highest 5% (about 432 samples, or 36 hours of peaks) and bills on the highest remaining sample. Many providers sample inbound and outbound separately and bill on the higher of the two; your contract defines the method.

Why can't the calculator give my exact 95th percentile?

Monthly volume only tells you the average rate. The 95th percentile depends on how the traffic is spread across the month: the same 100 TB can be a steady 309 Mbps or quiet nights and busy afternoons with a much higher 95th. The ratio you enter is an estimate. Your provider's usage graphs or an SNMP or flow tool on your own router give the real figure.

What is the difference between commit and burst?

The commit, or committed data rate, is the Mbps you agree to pay for every month whether or not you use it, usually at a lower price per Mbps. Burst is usage above the commit, billed per Mbps of 95th percentile above it, usually at a higher rate. A commit set too high wastes money every month; one set too low pays the burst rate on traffic you have every month.

When is a flat-rate port cheaper than burstable billing?

When the flat or unmetered price is below what your burstable bill would be for your traffic. The calculator shows that break-even once you enter a commit and prices. Flat-rate tends to win when your 95th percentile sits close to the port size most months; burstable tends to win when traffic is low with occasional peaks, because the top 5% of samples are free.