Subnet Calculator (IPv4 / CIDR)
Network
Give it an IPv4 address with CIDR (like 192.168.1.0/24) and it returns the network address, broadcast, netmask, wildcard mask, first/last usable host, host count, and IP class. Also detects RFC 1918 private ranges (10/8, 172.16/12, 192.168/16), loopback (127/8), and link-local (169.254/16). Includes a binary view so you can see how the mask aligns. Handles /31 (point-to-point) and /32 (single host) edge cases correctly.
Network
192.168.1.0/24
Netmask
255.255.255.0
Broadcast
192.168.1.255
Wildcard
0.0.0.255
First host
192.168.1.1
Last host
192.168.1.254
Usable hosts
254
CIDR
/24 (24 net bits, 8 host bits)
Class
C
Range
Private / reserved
Binary
All math is 32-bit unsigned. Default CIDR is /32 if you only enter an address. RFC 1918 ranges and loopback are flagged.
How to use
- Enter an IPv4 address with optional CIDR (e.g. 10.0.5.42/16, or 8.8.8.8 for /32).
- Read the network address, broadcast, and usable host range.
- Check whether the IP is in a private range before exposing it externally.
Frequently asked questions
- Why are first/last host different from network/broadcast?
- In a regular /N subnet, the lowest address is the network ID and the highest is the broadcast — both are reserved. Usable hosts run from network+1 to broadcast−1. /31 and /32 are exceptions (RFC 3021).
- What's the wildcard mask for?
- It's the bitwise NOT of the netmask, used by Cisco ACLs. 255.255.255.0 ↔ 0.0.0.255. ACL rules like 'permit 192.168.1.0 0.0.0.255' match the same range as a /24 subnet.
- Does it work for IPv6?
- No, IPv4 only. IPv6 has very different semantics — 128-bit addresses, no broadcast (uses multicast), no traditional 'classes', and prefixes commonly /48, /56, /64. A separate tool is needed.
- Why does 10.0.0.0/8 show ~16M hosts?
- 2^(32−8) − 2 = 16 777 214 usable hosts. The /8 means 8 network bits + 24 host bits. Real networks subdivide this — nobody routes a flat /8 in practice.
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