IPv4 Subnet Calculator

What does this tool do?

An IPv4 address has four octets from 0 to 255. The CIDR prefix tells how many of its 32 bits identify the network. This calculator finds subnet boundaries and capacity: use it to review configurations, plan ranges and study addressing. It calculates locally without inspecting your network.

How to use it

1. Enter the address in IPv4 and an integer prefix from 0 to 32 in CIDR, without the slash. For the example, use 192.168.10.42 and 26.
2. Select Calculate subnet. The mask separates network and host bits; the wildcard mask is its inverse.
3. Read Network as the lower boundary and Broadcast as the upper boundary. In conventional subnets, these addresses are reserved and the host range lies between them.
4. Review the first and last host, total addresses and usable hosts. Copy the result and check it against your network design.

Input and output examples

192.168.10.42/26

Network: 192.168.10.0
Broadcast: 192.168.10.63
Subnet mask: 255.255.255.192
Wildcard mask: 0.0.0.63
First host: 192.168.10.1
Last host: 192.168.10.62
Total addresses: 64
Usable hosts: 62

Important limitations

• Supports only IPv4 and integer prefixes from 0 to 32. IPv6, dotted masks as CIDR input and hostnames are not supported.
• For /31, both addresses are treated as usable on a point-to-point link. Broadcast shows the arithmetic upper boundary, not an operational broadcast on that link. For /32, network, broadcast and the single host are the same address.
• For /0, the entire IPv4 space is included. Counts are arithmetic: special ranges, reserved addresses, gateways and DHCP allocations are not deducted.
• Does not detect active devices, connectivity, conflicts, routes or address availability.

Common mistakes

• Pasting the address with /26 into IPv4 instead of separating address and prefix.
• Leaving CIDR empty, entering fractions or using a value outside 0–32.
• Using octets above 255, omitting an octet or adding leading zeros such as 010.
• Treating the calculated range as free addresses or assigning network and broadcast as hosts in a conventional subnet.

Frequently asked questions