Comment utiliser : Subnet Calculator
- Type an address with a prefix (
/24) or with a dotted subnet mask. - Read the network, broadcast and usable host range.
- Enter a longer prefix under Split into subnets to list every subnet of that size.
How subnetting works
An IPv4 address is 32 bits. The prefix length (the number after the slash in CIDR notation) says how many of those bits identify the network; the rest identify hosts. A /24 leaves 8 host bits: 256 addresses, of which the first is the network address and the last the broadcast address, leaving 254 usable hosts.
CIDR cheat sheet
| Prefix | Subnet mask | Addresses | Usable hosts |
|---|---|---|---|
| /8 | 255.0.0.0 | 16,777,216 | 16,777,214 |
| /16 | 255.255.0.0 | 65,536 | 65,534 |
| /22 | 255.255.252.0 | 1,024 | 1,022 |
| /24 | 255.255.255.0 | 256 | 254 |
| /26 | 255.255.255.192 | 64 | 62 |
| /28 | 255.255.255.240 | 16 | 14 |
| /30 | 255.255.255.252 | 4 | 2 |
| /31 | 255.255.255.254 | 2 | 2 (point-to-point, RFC 3021) |
| /32 | 255.255.255.255 | 1 | 1 (single host) |
Private and special ranges
- 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16 — private networks (RFC 1918), not routed on the internet.
- 100.64.0.0/10 — carrier-grade NAT shared space.
- 169.254.0.0/16 — link-local, used when DHCP fails.
- 192.0.2.0/24, 198.51.100.0/24, 203.0.113.0/24 — reserved for documentation.
Wildcard masks and cloud networks
A wildcard mask is the inverse of the subnet mask (0.0.0.255 for a /24) and is used in Cisco ACLs and OSPF. When planning AWS VPCs or Azure VNets, remember that the cloud reserves extra addresses: AWS keeps five per subnet (network, router, DNS, future use and broadcast).
IPv6
IPv6 addresses are 128 bits. Networks almost always use a /64 per LAN; ISPs hand out /48 or /56 blocks to customers, giving 65,536 or 256 LANs. Enter an IPv6 CIDR above to see the expanded form and range. Look up which addresses a name resolves to with the DNS lookup, or find your own public IP with What is my IP.
Private IP address ranges
These ranges are reserved for private networks (RFC 1918) and other special uses, so they’re never routed on the public internet. Paste any of them into the calculator above to see their full host range.
| Range | CIDR | Addresses | Used for |
|---|---|---|---|
| 10.0.0.0 – 10.255.255.255 | 10.0.0.0/8 | 16,777,216 | Private networks (RFC 1918) — large companies, cloud VPCs |
| 172.16.0.0 – 172.31.255.255 | 172.16.0.0/12 | 1,048,576 | Private networks (RFC 1918) — Docker’s default bridge uses 172.17.0.0/16 |
| 192.168.0.0 – 192.168.255.255 | 192.168.0.0/16 | 65,536 | Private networks (RFC 1918) — home and office routers |
| 100.64.0.0 – 100.127.255.255 | 100.64.0.0/10 | 4,194,304 | Carrier-grade NAT (RFC 6598), also Tailscale |
| 169.254.0.0 – 169.254.255.255 | 169.254.0.0/16 | 65,536 | Link-local (automatic addresses when DHCP fails) |
| 127.0.0.0 – 127.255.255.255 | 127.0.0.0/8 | 16,777,216 | Loopback (localhost) |
| fc00:: – fdff:ffff:… | fc00::/7 | — | IPv6 unique local addresses (the IPv6 private range) |
| fe80:: – febf:ffff:… | fe80::/10 | — | IPv6 link-local |
To see the public address your network uses on the internet, open What Is My IP.
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