IPv4 IPv6 Subnet Calculator
Calculate network, broadcast, host range, and usable addresses from CIDR notation for IPv4 and IPv6.
IPv4 and IPv6 CIDR subnet calculator
Network planning starts with CIDR notation such as 10.0.0.0/8 or
2001:db8::/32. This calculator accepts either address family, derives the network
and broadcast bounds, and estimates usable host counts (IPv4 subtracts network and broadcast
for prefixes /30 and shorter).
How to use this calculator
- Enter an IPv4 or IPv6 network address followed by
/prefix. - Review usable hosts in the summary card.
- Copy the JSON breakdown for documentation or change requests.
For IPv4-only CIDR math with dotted masks, see the CIDR Calculator. To test whether an IP falls inside multiple ranges, use IP CIDR Membership Checker.
Frequently Asked Questions
Does this support compressed IPv6?
Yes. Notation with :: and embedded IPv4 tails (for example 2001:db8::192.0.2.1/96) is expanded before math runs.
How are IPv6 host counts calculated?
IPv6 reports total address space size as a decimal string because usable host math is not limited by broadcast semantics the way IPv4 /24 networks are.
Is anything sent to a server?
No. Parsing and bigint math run locally in JavaScript.
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