Supernet and route summarization calculator
Paste several networks and get the smallest single CIDR block that covers them all. Ideal for route summarization and cleaner routing tables.
Enter the routes you want to summarize. SubnetKit finds the smallest single prefix that covers them all.
The summary route is the tightest single block that contains every input. It may include addresses beyond your inputs if they are not perfectly contiguous.
Summarizing many routes into one
Supernetting is subnetting in reverse. Instead of splitting a block into smaller pieces, you merge adjacent blocks into one shorter prefix. A router that would otherwise advertise four separate /24 routes can advertise a single /22, cutting three entries out of every table that learns it.
This calculator finds the tightest covering prefix for whatever you paste. If the inputs are perfectly contiguous and aligned, the summary is exact. If they have gaps, the summary still covers them but includes the addresses in between, and the tool shows you that full range so there are no surprises. To go the other way and split a block, use the CIDR calculator.
Do this from the terminal
The same reference data is a keyless JSON endpoint, and there are good local tools that need no network at all.
# summarise a set of blocks locally:
ipcalc 198.51.100.0/26 198.51.100.64/26
# or check the covering prefix against the reference table:
curl -s https://subnetkit.dev/api/cidr/24.json | jq '{mask, totalHosts}'Aggregation only works when the blocks are contiguous and start on a boundary of the covering prefix. If the result covers more than you put in, that is why.
The SubnetKit API is the one to reach for in a build step or a script. It has no key and no rate limit, and the full schema is in the OpenAPI document.
Frequently asked questions
What is supernetting?
Supernetting, or route summarization, combines several adjacent networks into one shorter prefix. Four contiguous /24s can become a single /22, which keeps routing tables small.
How do I summarize routes?
Find the smallest single prefix whose block contains all the input networks. This calculator does that automatically: paste the blocks and it returns the covering CIDR.
What if my networks are not contiguous?
The summary route is still the tightest block that covers them all, but it may include extra addresses between the gaps. The calculator shows the exact range it covers so you can check.
Is a supernet the same as an aggregate route?
Yes. A supernet, an aggregate route, and a summary route all mean one shorter prefix that represents several longer ones. It is the opposite of subnetting.