IP Subnet Calculator (IPv4 & IPv6)

How to use this subnet calculator

1. Type an IP address with its prefix, such as 192.168.1.130/26, or with a subnet mask, such as 192.168.1.130 255.255.255.192. If you type only the address, choose the prefix from the list next to it. The result updates as you type.
2. Read the result: the network address, the broadcast address, the first and last usable host, how many hosts fit, the subnet mask, the wildcard mask (used in Cisco ACLs and OSPF), the IP class and whether the address is private, public or special.
3. Binary view: the green bits are the network part, the grey bits are the host part. This is the easiest way to see why a subnet starts and ends where it does.
4. Check an IP to see if it belongs to the subnet, for example before you add a firewall rule.
5. Split the network into equal smaller subnets, for example a /24 into four /26 networks for different VLANs.
6. IP range to CIDR converts a range like 10.0.0.5 – 10.0.0.20 into the CIDR blocks you can paste into a firewall or a cloud security group.

IPv6 works the same way: type an address such as 2001:db8::1/64. Use Copy link to share a result; the address is kept in the link. Nothing you type is sent to a server.

How subnetting works

An IPv4 address has 32 bits, written as four numbers from 0 to 255. The prefix length (the number after the slash) says how many of the first bits name the network. The rest of the bits number the hosts inside that network. In 192.168.1.130/26, the first 26 bits are the network and the last 6 bits are for hosts, so the subnet has 2⁶ = 64 addresses.

The subnet mask is the same information written as an address: 26 ones followed by 6 zeros, which is 255.255.255.192. The wildcard mask is the opposite (zeros for the network, ones for the hosts): 0.0.0.63.

Example: 192.168.1.130/26 by hand

1. Block size = 256 − 192 = 64. The /26 subnets in the last number start at 0, 64, 128 and 192.
2. 130 is between 128 and 191, so the network address is 192.168.1.128.
3. The broadcast address is the last address of the block: 128 + 64 − 1 = 192.168.1.191.
4. The usable hosts are everything in between: 192.168.1.129 to 192.168.1.190, which is 64 − 2 = 62 hosts.

The rule behind it: the network address is the IP AND the mask, and the broadcast address is the network address OR the wildcard mask. Two addresses are always reserved (network and broadcast), so a subnet has 2^{(32 − prefix)} − 2 usable hosts. The exceptions are /31, which has 2 usable addresses for point-to-point links (RFC 3021), and /32, which is a single host.

IPv4 CIDR cheat sheet

Every prefix from /8 to /32 with its subnet mask, wildcard mask and size. The most common ones in home and office networks are /24 (254 hosts), /16 and, for links between two routers, /30 and /31.

Private and special IP address ranges

These ranges are reserved and are not routed on the public internet. The calculator shows the matching type for any address you enter.

IPv6 subnets in short

An IPv6 address has 128 bits, written as eight groups of four hex digits, such as 2001:0db8:0000:0000:0000:0000:0000:0001. Leading zeros in a group can be left out, and one run of zero groups can be replaced by ::, so the same address is 2001:db8::1.

The usual sizes are different from IPv4: a single LAN is almost always a /64 (the last 64 bits are the interface ID, needed for SLAAC). A home or small site usually gets a /56 or /48 from the provider, which is 256 or 65,536 /64 networks. IPv6 has no broadcast address, so every address in the range can be used. Common prefixes: fe80::/10 link-local, fc00::/7 unique local (the IPv6 version of private addresses), 2000::/3 global unicast, ff00::/8 multicast and 2001:db8::/32 for documentation.

More developer tools