IPv4 & IPv6 Subnet Calculator
Private by design — runs entirely in your browser
Enter an IPv4 or IPv6 CIDR like 192.168.1.0/24 and immediately see the network address, broadcast, first/last usable host, subnet mask, wildcard mask, and the count of usable hosts. Quick preset chips cover the prefixes engineers reach for most often.
How CIDR notation works
A CIDR like 10.0.0.0/16 splits the address into two parts. The number after the slash is the prefix length — the count of leading bits that identify the network. Everything after those bits identifies the host inside the network. A /16 keeps 16 bits for the network and leaves 16 bits for hosts, so the subnet covers 65,536 IPv4 addresses. IPv6 follows the same logic on a 128-bit address, which is why a /48 carries 80 host bits and an astronomical number of addresses.
What you get back
Network address — the all-zero host portion that identifies the subnet. Broadcast — the all-ones host portion, reserved in IPv4. First and last usable hosts — the range you can actually assign to devices. Subnet mask — the dotted-decimal form of the prefix. Wildcard mask — the inverse, used in router ACLs. Usable hosts — total addresses minus network and broadcast in IPv4, or the full count in IPv6.
Local-only computation
The math happens inside this page using bigint arithmetic. Your CIDR string is never sent to a Toova server, never logged, and never cached. Open the DevTools Network tab while typing — you will not see a single request leaving the browser. This makes the tool safe to use against private RFC 1918 ranges, internal data-center subnets, and any other network description you would not paste into a public web form.
Frequently Asked Questions
- What does /24 mean in 192.168.1.0/24?
- It is the prefix length: 24 bits identify the network and 8 bits identify hosts. That leaves 256 total addresses, with 254 usable host slots once the network and broadcast addresses are reserved.
- Why is the broadcast address not in the usable range?
- IPv4 reserves the all-zero host portion as the network address and the all-ones host portion as the broadcast. Hosts cannot be assigned those values. IPv6 has no broadcast, so every address inside the prefix is assignable.
- How does this handle /31 and /32?
- /32 means a single host. /31 is the point-to-point convention from RFC 3021 where both addresses are usable host endpoints — there is no broadcast since only two hosts exist.
- Can I use this for IPv6?
- Yes. Paste a CIDR like 2001:db8::/48 to see the network address, the first and last address inside the prefix, and the total count. The wildcard and broadcast fields are blank for IPv6 since the concept does not exist there.
- Does the tool log my CIDR input?
- No. The math runs entirely inside the browser using native BigInt arithmetic. Nothing is sent to a Toova server, not even page analytics on the input itself.
- Can I plan a VLSM layout with this?
- Yes — calculate each segment individually. Run the tool on the parent /20 to see its range, then on each child /24 or /28 to see where they fit. The values are exact, so you can validate plans before applying them.