IP Subnet Calculator

How the subnet calculator works

An IPv4 address is 32 bits. A subnet mask splits those bits in two: the bits under the 1s of the mask name the network, and the bits under the 0s name a host on that network. In 192.168.1.10/24, the /24 means the first 24 bits are the network, which is the same as the mask 255.255.255.0. That leaves 8 host bits, or 256 addresses from 192.168.1.0 to 192.168.1.255.

The subnet calculator does that bit math for you. The network address is the IP with every host bit set to 0, and the broadcast address is the IP with every host bit set to 1. Neither can be given to a device, so a /24 has 254 usable hosts. The wildcard mask is the subnet mask inverted, the form Cisco ACLs and OSPF network statements expect. Type a mask such as 10.0.0.1 255.255.240.0 instead of a prefix and the calculator converts it, and it reads IPv6 addresses like 2001:db8::/48 as well.

Subnet mask cheat sheet

Every IPv4 prefix from /8 to /32 with its subnet mask, wildcard mask and size. Each step down halves the number of addresses.

Private and reserved IPv4 ranges

These ranges are never routed on the public internet. The calculator labels any address that falls in one of them.

How to use

1. Type an address with its prefix, like 10.20.30.40/20, or with a subnet mask, like 10.20.30.40 255.255.240.0.
2. Or type just the address and pick the prefix from the list. The list shows the matching subnet mask for each prefix.
3. Read the network, broadcast and host range from the results. Click Copy on any row, or Copy All for the whole set.
4. To plan smaller networks, choose a size under Split into. The table lists every subnet with its host range, and Copy list copies the CIDR blocks one per line.

Frequently Asked Questions