Bandwidth calculator
for ISPs
Work out the upstream capacity your subscribers need, and see the arithmetic that got there. It runs in your browser: nothing you type is sent anywhere.
Size your upstream
Capacity sold, divided by the contention ratio you plan on. Concurrency is shown against the answer rather than divided into it.
Everyone the link has to carry.
The download speed you sell them.
Your own policy: there is no standard figure to copy.
Online at once in your busiest hour. Leave it blank if you do not know.
400 × 8 Mbps = 3,200 Mbps sold ÷ 8 = 400 Mbps
- Capacity sold
- 3.2 Gbps400 subscribers × 8 Mbps
- Carried at once
- 12.5% What 1:8 says the link holds at any one moment
- Peak-hour ceiling
- 1.3 Gbps If every 40% online saturated their package together
- Covers
- 31.3% Of that ceiling: the bet oversubscription makes
What the model assumes
Contention and concurrency are different claims, and conflating them is how an upstream gets undersized.
Capacity sold
Every subscriber multiplied by the speed on their package. It is the one figure in the calculation that is not an assumption: it is what you have already promised.
Contention ratio
How many megabits you sell for every megabit of upstream you buy. At 1:8 the link carries an eighth of what you sold at any one moment, and the other seven eighths rest on subscribers not all pulling at once.
Peak-hour concurrency
The share of your subscribers online in the busiest hour. It is shown against the result and never divided into it: a contention ratio is already a statement about simultaneous use, so dividing by both counts the same discount twice and undersizes the link.
What it leaves out
Protocol overhead, the shape of your traffic, caching and CGNAT, and any one subscriber able to saturate the link alone. Size the upstream from the result, then correct it against your own peak-hour graphs.
The model is one line: subscribers × package speed, divided by the contention ratio. That ratio is your own policy rather than a published standard, and the figures above are prefilled to show the arithmetic, not to recommend a number. A network of heavy users and one of light users are sized differently at the same subscriber count, and the only thing that settles it is what your upstream actually carries in your own busiest hour.
See how dedicated capacity is deliveredSizing an upstream
There is no industry figure to copy. The honest way to set one is backwards: measure what your upstream actually carries in your busiest hour, divide the capacity you have sold by that, and you have the ratio your network is already running at. Plan the next link from it.
Not on its own. Oversubscription is how every ISP is built, because subscribers are idle most of the time and an upstream sized for all of them at once would sit unused. A ratio becomes a problem when the link saturates in the peak hour and stays there.
Because the contention ratio already carries that assumption. 1:8 is a claim that an eighth of what you sold is in use at any moment. Dividing a 40% concurrency in as well would size the link for about 5% of what you sold, and it would saturate on the first busy evening.
Dedicated capacity is normally quoted as one symmetrical figure, so the result sizes the link rather than a direction. If you sell asymmetric packages, run the calculation on the download speed, which is the larger side.
The result sizes the subscribers you have now. Run it again with the count you expect in a year: capacity can be added on the same link later, so it is worth knowing the second figure before the first one is commissioned.
Capacity, and the billing on top of it
Centipid runs the billing, the routers and the subscriber access for internet providers in 27 countries.