Subnet / CIDR calculator

Enter an IPv4 address with a CIDR prefix (e.g. 10.0.0.0/24) to get the network, broadcast, usable host range, and host count.

How to use the subnet / cidr calculator

  1. Enter an IPv4 address with a CIDR prefix, e.g. 10.0.0.0/24.
  2. Press Calculate.
  3. Read the network, broadcast, host range, and host count.

Reading the results

The CIDR prefix (e.g. /24) says how many leading bits identify the network; the rest address hosts. The network address is the first in the range and the broadcast is the last — neither is assignable to a device, which is why a /24 has 256 total addresses but 254 usable. Calculated entirely in your browser.

Code & API examples

Use this from the command line or your code.

Shell (ipcalc)
ipcalc 10.0.0.0/24
Python
import ipaddress
n = ipaddress.ip_network('10.0.0.0/24')
print(n.network_address, n.broadcast_address, n.num_addresses)

See all endpoints at /api/tools/.

Frequently asked questions

The /24 is the CIDR prefix — it says the first 24 bits are the network portion, leaving 8 bits (254 usable addresses) for hosts.

The network address is the first address in the range (identifies the subnet); the broadcast address is the last (used to reach every host at once). Neither is assignable to a device.

CIDR (Classless Inter-Domain Routing) writes a network as an address plus a prefix length, like 10.0.0.0/24. The prefix says how many leading bits are fixed as the network, replacing the old class A/B/C system.

A /26 leaves 6 host bits, giving 64 total addresses and 62 usable ones after subtracting the network and broadcast addresses.

Take 32 minus the prefix to get the host bits, raise 2 to that power for total addresses, then subtract 2 for the network and broadcast addresses (e.g. /28 gives 2^4 = 16 minus 2 = 14 usable).

A subnet mask like 255.255.255.0 marks the network bits with 1s; it's just another way to write the prefix. 255.255.255.0 equals /24 — both say the first 24 bits are the network.

The first address identifies the network itself and the last is the broadcast address, so neither can be assigned to a host. That's why a /24 has 256 addresses but only 254 are usable.

A /30 gives 4 addresses with 2 usable, ideal for point-to-point links. A /31 (2 addresses, both usable) is allowed for point-to-point per RFC 3021, and /32 designates a single host.

Borrow host bits by increasing the prefix: a /24 becomes two /25s, four /26s, and so on. Each added bit halves the host count while doubling the number of subnets.

RFC 1918 reserves 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 for internal use. They're not routable on the public internet, so devices behind them share a public IP via NAT.

No. It runs entirely in your browser, so the addresses you enter never reach a server. That fits vpn.golf's no-logs approach — nothing to record because nothing leaves your device.

WireGuard often assigns each device a single tunnel address as a /32 (or /128 for IPv6) so traffic is routed to exactly one peer. It pins one address per device rather than a whole subnet.
Related tools
IP address lookup What is my IP address?
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