Subnet Calculator

Enter an IPv4 address with a CIDR prefix or subnet mask to see its network, broadcast address, usable host range and more, plus a full prefix reference table.

You can also type CIDR straight into the address box, like 10.0.0.0/22 or 10.0.0.5 255.255.252.0.

Network
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How subnetting works

An IPv4 address is 32 bits, shown as four numbers from 0 to 255. The prefix length says how many of those bits belong to the network; the rest identify hosts. The calculator applies the mask with bitwise AND to find the network address, then sets all host bits to 1 for the broadcast address.

Network = IP AND mask
Broadcast = network OR (NOT mask)
Total addresses = 2^(32 − prefix) · Usable hosts = total − 2

Worked example

For 10.0.0.5/22 the mask is 255.255.252.0. The network is 10.0.0.0, the broadcast is 10.0.3.255, and usable hosts run from 10.0.0.1 to 10.0.3.254: 2¹⁰ − 2 = 1,022 hosts.

CIDR reference table

PrefixSubnet maskAddressesUsable hosts
/8255.0.0.016,777,21616,777,214
/16255.255.0.065,53665,534
/20255.255.240.04,0964,094
/22255.255.252.01,0241,022
/23255.255.254.0512510
/24255.255.255.0256254
/25255.255.255.128128126
/26255.255.255.1926462
/27255.255.255.2243230
/28255.255.255.2401614
/29255.255.255.24886
/30255.255.255.25242
/31255.255.255.25422
/32255.255.255.25511

Need unique IDs for devices or records? Try the UUID generator.

Last reviewed October 2026.

Frequently asked questions

What does a subnet calculator do?

It takes an IPv4 address and a prefix length (like /24) or subnet mask (like 255.255.255.0) and works out the network address, broadcast address, the range of usable host addresses and how many hosts the subnet can hold.

What is CIDR notation?

CIDR (Classless Inter-Domain Routing) writes a network as an address followed by a slash and the number of network bits, such as 192.168.1.0/24. The /24 means the first 24 bits are the network part, which is the same as a 255.255.255.0 mask.

Why are two addresses not usable?

In a normal subnet, the first address identifies the network and the last is the broadcast address, so hosts can't use them. A /24 has 256 addresses but 254 usable hosts. /31 (point-to-point links) and /32 (single host) are special cases where every address is usable.

What is a wildcard mask?

A wildcard mask is the inverse of the subnet mask: 0.0.0.255 for a /24. It is used in access control lists and routing protocols such as OSPF on many routers.

Which addresses are private?

RFC 1918 reserves 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 for private networks. These are not routed on the public internet. The calculator also flags loopback (127.x), link-local (169.254.x) and carrier-grade NAT (100.64.0.0/10) ranges.