Subnet calculator
Addresses are worked out in this tab. Nothing is sent.
- 10.0.0.5/32
- 10.0.0.6/31
- 10.0.0.8/29
- 10.0.0.16/30
- 10.0.0.20/32
How to use this tool
Work out an IPv4 subnet from CIDR notation, or turn an address range into CIDR blocks.
Type an address with a prefix
Enter 192.168.1.10/24, or an address and a netmask separated by a space. The block is normalised to its network address.
Read the subnet details
Network, broadcast, mask, wildcard, first and last host, total and usable host counts appear as you type.
Convert a range to CIDR
Enter the first and last address on the right to get the smallest list of CIDR blocks that covers exactly that range, ready to copy.
FAQ
What does /24 mean?
The number after the slash is how many leading bits are the network. /24 leaves 8 bits for hosts: 256 addresses, mask 255.255.255.0.
Why are usable hosts two fewer than the total?
The first address is the network and the last is the broadcast, so a normal subnet cannot give them to hosts. /31 is the exception (two usable, for point-to-point links, RFC 3021) and /32 is a single host.
Can I type a netmask instead of a prefix?
Yes. Type an address and a mask with a space, such as 10.1.2.3 255.255.252.0. A bare address is read as /32.
What does the range to CIDR box do?
It covers a start and end address with the fewest CIDR blocks. 10.0.0.5 to 10.0.0.20 becomes 10.0.0.5/32, 10.0.0.6/31, 10.0.0.8/29, 10.0.0.16/30 and 10.0.0.20/32.
Does it support IPv6 or send my addresses anywhere?
IPv4 only for now. Everything is calculated in this tab; nothing is sent.