Subnet Calculator
Network, broadcast and host count from IP and prefix.
How to use Subnet Calculator
Compute network address, broadcast address and usable host count from an IP and CIDR prefix.
Open Subnet Calculator on toolpermarket — the form is ready, so type your numbers and read the result.
In the IP address field, enter an IPv4 address like 192.168.1.10. Four numbers separated by dots.
In the Prefix field, enter the CIDR prefix from 0 to 32. A /24 covers 256 addresses.
Press Calculate to compute the result. The output appears immediately below the form. Edit a value and press the button once more to see the updated answer.
Read the result and use it as needed. If the number looks off, re-check your inputs and run it again — the math is deterministic, so the same entries always return the same answer.
Worked example. 192.168.1.10 with prefix /24 gives network 192.168.1.0, broadcast 192.168.1.255, and 254 usable hosts.
Tips for accurate results.
Prefix /24 is the common small-network size.
Usable hosts exclude network and broadcast.
/31 and /32 are special point-to-point cases.
When to use Subnet Calculator. Working out a subnet for a network. Finding the usable host range. Checking an IP belongs to a block.
When you actually reach for this
- You want the network and broadcast addresses, host range and mask from a CIDR.
- You are splitting or sizing an IPv4 block.
Where this tool stops being accurate
- It is IPv4 classless (CIDR) math; it does not reserve addresses the way some cloud providers do in practice.
- A /31 is a special two-address point-to-point case the basic host-count formula does not fit.
Frequently asked questions
What is the difference between network and broadcast?
The network address identifies the subnet itself and the broadcast address is the last address, used to reach every host at once. Usable hosts sit between them, so a /24 has 254 addresses people can actually assign.
Why does a /24 have 254 usable hosts, not 256?
Because the first address is the network address and the last is the broadcast address; neither can be a host. That leaves 256 minus 2 equals 254 usable addresses.
What about /31 and /32?
Those are special. A /31 has two addresses used as a point-to-point link, and a /32 is a single host. The tool reports the conventional usable count and notes when the prefix is one of these edge cases.
How many usable hosts?
For most prefixes it is two to the power of host bits minus two (network and broadcast), except special small blocks.
What does the CIDR number mean?
It is the count of network bits in the mask; a bigger number means a smaller subnet with fewer hosts.