What does CIDR notation mean (the `/24`)?

The number after the slash is how many bits of the IP are the network prefix. /24 fixes the first 24 bits (network) and leaves the last 8 bits free → 256 addresses. /16 fixes the first 16 bits → 65,536 addresses. Smaller number = bigger network.

Why is Total Hosts = 2^n − 2?

Two addresses in every IPv4 subnet are reserved: the network address (all-zero host bits, e.g. 192.168.1.0 in a /24) and the broadcast address (all-one host bits, e.g. 192.168.1.255). Neither can be assigned to a device. Total usable hosts = 2^(32 − prefix) − 2.

/31 and /32 show weird host numbers. Why?

For /31 only 2 addresses exist, both are technically network and broadcast by the old rule, so the formula gives 0 usable hosts. RFC 3021 specifically allows /31 for point-to-point links, treating both as usable. /32 means exactly one address (a single-host route). The first / last host fields are not meaningful for /31 or /32, they are edge cases.

What's a wildcard mask?

The bitwise inverse of the subnet mask. /24 mask is 255.255.255.0, wildcard is 0.0.0.255. Cisco ACLs use wildcard masks instead of regular masks. The tool surfaces the same information indirectly through the broadcast address.

Where is the calculation done?

Entirely in your browser, pure JavaScript bit math. Nothing leaves your device. For IPv6 use IPv6 Calculator.

Free, no signup, no rate limit (everything runs client-side).

Utility

IPv4 Calculator

IPv4 subnet calculator

Input

IP Address

CIDR Notation

Calculate network ranges, broadcast addresses, and netmasks from CIDR notation (e.g., /24).

Terminal

Console ready. Execute a command to see output...

About IPv4 Calculator

Mastering the Subnet

Subnetting divides a network into smaller, efficient pieces. This tool accepts CIDR notation (192.168.1.1/24) and breaks it down.

Key Outputs

Network Address: The identifier of the subnet.
Broadcast Address: The address used to talk to everyone in that subnet.
Host Range: The usable IPs for devices.

Private Ranges (RFC 1918)

10.x.x.x: Large enterprise networks.
172.16.x.x: AWS/Cloud defaults.
192.168.x.x: Home routers.

How to use IPv4 Calculator

Enter the IPv4 address
For example 192.168.1.10. Any host inside the subnet works.
Enter the CIDR prefix length
A number 0 to 32 (without the slash). 24 is typical for home networks, 30 is a 2-host point-to-point.
Hit Calculate
Subnet mask, network address, broadcast, first / last usable host, and total host count appear in the terminal panel.

Frequently Asked Questions

: The number after the slash is how many bits of the IP are the network prefix. /24 fixes the first 24 bits (network) and leaves the last 8 bits free → 256 addresses. /16 fixes the first 16 bits → 65,536 addresses. Smaller number = bigger network.
: Two addresses in every IPv4 subnet are reserved: the network address (all-zero host bits, e.g. 192.168.1.0 in a /24) and the broadcast address (all-one host bits, e.g. 192.168.1.255). Neither can be assigned to a device. Total usable hosts = 2^(32 − prefix) − 2.
: For /31 only 2 addresses exist, both are technically network and broadcast by the old rule, so the formula gives 0 usable hosts. RFC 3021 specifically allows /31 for point-to-point links, treating both as usable. /32 means exactly one address (a single-host route). The first / last host fields are not meaningful for /31 or /32, they are edge cases.
: The bitwise inverse of the subnet mask. /24 mask is 255.255.255.0, wildcard is 0.0.0.255. Cisco ACLs use wildcard masks instead of regular masks. The tool surfaces the same information indirectly through the broadcast address.
: Entirely in your browser, pure JavaScript bit math. Nothing leaves your device. For IPv6 use IPv6 Calculator.
: Free, no signup, no rate limit (everything runs client-side).