Free Subnet / CIDR Calculator
Enter an IPv4 address and CIDR prefix to get the network address, broadcast address, usable host range, subnet mask, wildcard mask and total host count — everything a network engineer needs at a glance.
To expand a block into every address it contains, use CIDR to IPv4 Range; to check the network you are actually on, see What Is My IP.
How to use the Subnet Calculator
- 1 Enter an address in CIDR form, such as 192.168.1.0/24.
- 2 Read the network address, broadcast address, usable host range and subnet mask.
- 3 Check the host count to see how many devices the subnet can hold.
- 4 Try a different prefix length to see how the block size changes.
How to Use
Type an address like 192.168.1.10 and choose a prefix (or type 192.168.1.10/24). All the subnet details are calculated instantly.
- Network and broadcast addresses
- First and last usable host
- Subnet mask and wildcard mask
- Total addresses and usable hosts
- Binary view of the address and mask
Understanding CIDR
CIDR notation like /24 means the first 24 bits are the network portion and the remaining 8 bits identify hosts — 254 usable addresses. Larger prefixes mean smaller subnets. Use this calculator to plan addressing, verify firewall rules or troubleshoot routing.
Frequently asked questions
What does the /24 in an address mean?
It is the prefix length — the first 24 bits of the address identify the network, leaving 8 bits for hosts. So a /24 holds 256 addresses, of which 254 are usable, and it corresponds to the familiar 255.255.255.0 subnet mask.
Why are two addresses per subnet unusable?
The first address is the network identifier and the last is the broadcast address, so neither can be assigned to a host. That gives 2ⁿ − 2 usable addresses for a block of 2ⁿ — which is why a /24 yields 254, not 256.
Why do /31 and /32 behave differently?
They have no room for the usual reservation. A /32 is a single address used for a host route, and a /31 contains exactly two addresses, both usable — RFC 3021 allows this for point-to-point links, so the "minus two" rule does not apply to them.
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