Subnet Calculator
Type an IPv4 address and CIDR prefix — network address, broadcast address, subnet mask, and usable IP range are calculated automatically.
How to use the subnet calculator
- Type in an IPv4 address, e.g. 192.168.1.130.
- Choose a CIDR prefix (number of bits in the network portion, e.g. /24).
- The network address, broadcast address, subnet mask, and usable address range are calculated automatically.
What does the CIDR prefix mean?
CIDR notation (Classless Inter-Domain Routing) specifies how many of the 32 bits in an IPv4 address make up the network portion — written as a slash followed by a number, e.g. /24. A /24 network has 8 bits left for the host portion, giving 256 addresses total (254 usable, since the network address and broadcast address are reserved).
The network address identifies the network itself (all host bits set to 0), while the broadcast address is used to send to every device on the network at once (all host bits set to 1) — both are reserved and normally can't be assigned to a single device.
Frequently asked questions
Why are there two fewer usable addresses than the total?
Because the network address (all host bits = 0) and broadcast address (all host bits = 1) are reserved and can't be assigned to a single device — except for /31 and /32, which are used for special cases like point-to-point links.
Does this work for IPv6?
No, this tool only calculates IPv4 subnets.
Is the IP address I type sent to a server?
No, all calculation happens locally in your own browser — nothing is sent or stored anywhere.