How it works
The subnet calculator takes an IP address with its mask or CIDR prefix and computes everything that defines that network: network address, broadcast address, usable host range, total number of addresses, and the mask in its various notations. It works for both IPv4 and IPv6.
It avoids manual binary math when planning a network's addressing, splitting a block into smaller subnets, or checking whether an IP falls within a given range.
Use cases
- Plan a network's addressing and know how many hosts fit in each subnet.
- Split a large block into smaller subnets to separate segments or VLANs.
- Check the network and broadcast addresses before configuring routers or firewalls.
- Convert between CIDR notation (/24) and decimal mask (255.255.255.0).
Frequently asked questions
What does CIDR notation like /24 mean?
The number indicates how many bits, counted from the left, form the network part. In IPv4 a /24 reserves 24 bits for the network and leaves 8 for hosts, equivalent to the mask 255.255.255.0.
Why does a /24 have 256 addresses but only 254 hosts?
In IPv4 the first address of the range identifies the network and the last is the broadcast; neither is assigned to a host. That is why of the 256 addresses in a /24, 254 remain usable.
What is the broadcast address?
It is the last address of an IPv4 subnet and is used to send a message to all hosts on the segment at once. IPv6 has no broadcast: it uses multicast addresses instead.
Does the calculation change in IPv6?
The concept of a prefix is the same, but IPv6 uses 128 bits instead of 32 and does not reserve broadcast. Subnets are usually /64 and the number of addresses per network is enormous, so it is shown as a power of two.