Best free CIDR aggregation tools

AdminKit is built by Netbase JSC. AdminKit is listed below; NetworkCalc, subnet-calculator.org and VLANlab are independent and not affiliated with AdminKit.

What each tool’s own page confirms

NetworkCalc’s IP Range to CIDR tool, read 2026-11-09, states it can “turn an IP range into CIDR blocks, or merge a list of blocks.” Pasting multiple blocks “comma separated or one per line” produces a result where “adjacent and overlapping blocks are merged and the result is the smallest exact set of blocks” — the same minimal exact-cover aggregation AdminKit’s CIDR aggregator performs. NetworkCalc’s own page additionally shows, alongside that exact result, the single wider block that would cover everything “with the extra addresses it would add” — a second view AdminKit’s tool does not offer. NetworkCalc’s examples and documentation use IPv4 addressing only; nothing on the page mentions IPv6.

subnet-calculator.org’s Supernet Calculator, also read 2026-11-09, takes “one or multiple network IDs each in a separate line in CIDR notation format” and lets you “press aggregate to summarize the supernet of the input networks” — but its own worked example (four /24 networks combined into one /21) shows it always returns a single covering block, not the minimal set of multiple CIDR blocks that exactly reproduces the input. It is free, IPv4 only, with no stated account requirement.

VLANlab’s CIDR Merge and Aggregator, read 2026-11-09, states you can “paste a list of IPv4 or IPv6 CIDR blocks and merge overlapping or adjacent ranges into the smallest possible set of non-overlapping prefixes,” with each merged block “converted back to the minimal set of CIDR prefixes that cover it exactly” — the same exact-cover behavior as AdminKit’s and NetworkCalc’s tools, for both IPv4 and IPv6. Its own page states there is no login, no ads and no tracking.

Is CIDR aggregation the same as a subnet calculator?

No. A subnet calculator — compared separately in AdminKit’s best free subnet calculators roundup — takes one address or CIDR block and works out its network, broadcast and host range. CIDR aggregation, also called supernetting or route summarization, goes the other direction: it takes many addresses or blocks and finds the fewest CIDR prefixes that cover exactly the same addresses, collapsing adjacent, aligned ranges into one. A tool can do one without the other — NetworkCalc, subnet-calculator.org and VLANlab each also publish separate single-block subnet calculators, distinct from the aggregation tools compared on this page.

The honest angle

If you want to see both the exact-cover result and the single wider summary route side by side, NetworkCalc’s own page is the only one of the three that shows both. If you only need a quick single supernet for a handful of contiguous blocks and don’t need IPv6 or an exact multi-block result, subnet-calculator.org’s Supernet Calculator does that narrower job. If you need IPv6 aggregation alongside IPv4 in the same free tool, VLANlab’s CIDR Merge and Aggregator matches AdminKit’s own IPv4/IPv6 scope. AdminKit’s CIDR aggregator additionally separates exact duplicates from ranges already covered by a wider entered range as two distinct results, and its own tool page states the aggregation runs entirely in your browser’s JavaScript — a claim this comparison could not verify one way or the other for the other three tools, since none of their pages state their computation architecture.

CIDR aggregation is part of AdminKit’s IP & network cluster, alongside the subnet calculator and IP in CIDR checker — see the CIDR glossary entry for the notation itself.

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Trademarks belong to their respective owners; AdminKit is not affiliated with NetworkCalc, subnet-calculator.org or VLANlab.