Subnet calculator

Q: How many usable hosts are in a subnet?

A subnet with prefix length n has 2 to the power of (32 - n) addresses. Two are reserved, the network and broadcast addresses, so a /24 has 256 addresses and 254 usable hosts. A /31 has two usable addresses for point-to-point links, and a /32 is a single host.

Q: How do I check whether an IP is in a range?

Enter the range, then paste IP addresses into 'Check IPs against this range'. Each is marked inside or outside, which helps when checking firewall rules, allow-lists or whether a suspicious IP belongs to a known network.

Q: Does it work with IPv6?

Yes. Enter an IPv6 address and prefix such as 2001:db8::/48 to see the network, the last address, the total number of addresses and how many /64 networks it contains.

Work out the network, broadcast, usable range, mask, wildcard and host count for any IPv4 or IPv6 CIDR, and check which IPs fall inside it.

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IP address with prefix or mask

Try:

Network: 10.0.0.0/15
Subnet mask: 255.254.0.0
Wildcard mask: 0.1.255.255
First usable: 10.0.0.1
Last usable: 10.1.255.254
Broadcast: 10.1.255.255
Usable hosts: 131,070
Total addresses: 131,072
Binary mask: 11111111.11111110.00000000.00000000
Address type: Private (RFC 1918)
Previous range: 9.254.0.0/15
Next range: 10.2.0.0/15

Check IPs against this range

How it works

Enter an address with a prefix length (192.168.10.37/27), with a dotted mask (10.0.0.0 255.255.248.0) or an IPv6 prefix. The calculator shows the network and broadcast addresses, the usable range, the subnet and wildcard masks, the number of hosts, the mask in binary and the neighbouring ranges, and says whether the range is private, public, CGNAT, documentation or another special block.

Reference pages for every IPv4 prefix length:

Questions

How many usable hosts are in a subnet?

A subnet with prefix length n has 2^(32 − n) addresses. Two are reserved, the network and broadcast addresses, so a /24 has 256 addresses and 254 usable hosts. The exceptions are /31, where both addresses are usable on point-to-point links (RFC 3021), and /32, a single host.

What is a wildcard mask?

The inverse of the subnet mask: 0 bits must match and 1 bits can be anything. Cisco access lists and OSPF use wildcard masks, so a /24 mask of 255.255.255.0 is written 0.0.0.255.

How do I check whether an IP is in a range?

Enter the range, then paste IP addresses into “Check IPs against this range”. Each is marked inside or outside, which helps when reviewing firewall rules and allow-lists, or checking whether a suspicious IP belongs to a provider’s published range.

Does it work with IPv6?

Yes. Enter an IPv6 address with a prefix such as 2001:db8::/48 to see the network in short and expanded form, the last address, the total number of addresses and how many /64 networks it contains.