IP subnet calculator
IPv4 and IPv6 CIDR maths — network, broadcast, usable range, masks, special ranges, splitting, summarising, ranges to CIDRs, and reverse-DNS names.
Added · updated 28 October 2026
Works with
- DHCP, ARP, NAT and routing Networkits route lookup sends the router's prefixes and an address here, to the Contains tab
How to use it
Everything is computed in the page; nothing is looked up.
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Calculator: enter
192.168.10.77/26,10.0.0.1 255.255.255.0, a wildcard mask, or an IPv6 address with a prefix. You get the network, broadcast, usable range (with the /31 and /32 rules), masks, a binary view with the network bits highlighted, special-purpose ranges (RFC 1918, CGNAT, documentation, link-local, ULA, multicast and its scope…), the PTR name, and the reverse zones to delegate. -
Split: divide a network by new prefix, into N subnets, or by hosts needed per subnet; copy the list or download it as CSV.
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Summarise & ranges: merge overlapping and adjacent networks into the fewest CIDR blocks, and turn any start–end range into CIDR blocks.
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Contains: check a list of addresses against a list of networks.
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IPv6 & EUI-64: compress (RFC 5952) and expand addresses, and derive EUI-64 interface IDs and SLAAC / link-local addresses from a MAC address.
Sharing
Share link copies a URL that opens this tool exactly as configured. Each tab’s inputs travel with it: ?cidr= on Calculator, ?split=…&splitMode=count&splitN=4 on Split, ?nets=/?addrs= on Contains, ?v6=, ?mac=, ?pfx= on IPv6.
For example: subnet/?cidr=10.1.2.3/20.
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Runs entirely in your browser; nothing you type leaves this page.