A CIDR calculator for IPv4 and IPv6, in one place.
Type a CIDR — `10.0.0.0/24`, `2001:db8::/32`, anything — and see the network address, host range, netmask, wildcard, and host count. Auto-detects v4 vs v6. All math happens in this browser tab.
IPv410.0.0.0/2410.0.0.010.0.0.25510.0.0.110.0.0.254254255.255.255.00.0.0.255/24Pure arithmetic — IPv4 via 32-bit integers, IPv6 via BigInt — in this browser tab. No DNS lookups, no WHOIS, no network calls. We never see what you paste.
IPv4 and IPv6 in the same UI, with the math already done.
A calculator that auto-detects the address family, validates input strictly, and renders every common subnet field in one table — including the bits most calculators forget about for IPv6.
One input box, one output table — auto-detected by the colon-vs-dot heuristic, then validated against the correct family rules. No tab to flip.
Octets must be 0–255. Prefix must be 0–32 (v4) or 0–128 (v6). Compressed `::` notation is parsed, but only the legal one occurrence per address. Invalid input fails fast with a precise error.
Network address (host bits zeroed), broadcast (host bits set). Useful for confirming whether a given IP is the network number, the broadcast, or a usable host — common gotcha in firewall rules.
For IPv4 /24 and below: network and broadcast excluded, host count is `2^h - 2`. For /31 and /32: range collapses to point-to-point or single-host (RFC 3021 / 3627). For IPv6: full range, since broadcast does not apply.
Netmask (`255.255.255.0`) for ACLs, wildcard (`0.0.0.255`) for Cisco-style match rules. Same data, different representations.
Click any row to copy that field. Useful when generating Terraform variables or pasting into a firewall config one field at a time.
Every keystroke triggers a fresh parse and render. No Calculate button.
Use anonymously. No account, no history, no telemetry. Inspect the network tab — there is nothing outbound.
Wherever a subnet has to make sense.
Pick a `/16` for the VPC, then carve `/24`s for each AZ. The calculator confirms host counts and address ranges before you commit to a Terraform module.
Cisco and BSD-derived firewalls need wildcard masks instead of netmasks. Drop your CIDR in, copy the wildcard line — no off-by-one with bit inversion.
ISPs hand out `/56` or `/48` blocks. Verify how many `/64`s that gives you (256 from a /56, 65,536 from a /48) before assigning to teams.
"Is 10.42.7.99 inside 10.42.0.0/20?" Paste the subnet, see its range — first host through last. The answer is yes if the IP falls in the range.
RFC 3021 lets you use a /31 as a point-to-point link with both addresses usable. Verify host count = 2 and that no broadcast is reserved.
Some legacy systems insist on dotted netmask form (`255.255.252.0`) instead of CIDR prefix. Compute, copy, paste.
CIDR & subnetting, the plain answers.
Two addresses in every IPv4 subnet are reserved: the network address (all host bits zero) and the broadcast (all host bits one). Neither is usable for hosts. So a `/24` has 256 total addresses but only 254 usable. RFCs 3021 and 3627 carve out exceptions for `/31` and `/32` — see the next question.
`/32` is a single host — no range, just the address itself. `/31` is a special-case point-to-point link (RFC 3021): only two addresses, but both are usable since there is no need for broadcast on a P2P link. The calculator handles both correctly.
IPv6 abolished broadcast intentionally. Functions that needed broadcast on v4 (ARP, neighbor discovery, DHCP) use multicast or solicited-node addresses on v6. Tools that show a "broadcast" row for an IPv6 subnet are usually computing "highest address in range" and labeling it incorrectly.
A wildcard mask is the bitwise inverse of a netmask, used by Cisco IOS and a few other systems for ACL matching. `/24` → netmask `255.255.255.0` → wildcard `0.0.0.255`. The two encode the same information; which one your config wants depends on which vendor wrote the parser.
No. Parsing and arithmetic run entirely in this browser tab — IPv4 via 32-bit integer math, IPv6 via BigInt. There are no DNS lookups, no WHOIS calls, nothing outbound. Open DevTools → Network and watch nothing happen.
Not yet. The calculator currently shows a single subnet at a time. If you want to split a `/16` into specific smaller blocks (`/22` × 4, `/24` × 16, etc.) drop us a note via /contact — it is on the candidate list.
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