How do I find the network and broadcast address for an IP and CIDR prefix?

Enter an IPv4 address and set the Prefix between 0 and 32. The tool shows the Network address, Broadcast address, Usable host range, Subnet mask and Usable hosts. Calculations run locally in your browser.

Why does a /24 have 254 usable hosts instead of 256?

The first address is the network address and the last is the broadcast address, so two of the 256 total addresses are not usable. The tool lists both Total addresses and Usable hosts.

How are /31 and /32 prefixes handled?

They follow RFC 3021: /31 is treated as a point-to-point link and /32 as a single host. In these cases the broadcast address is shown as Not applicable.

How do I split a network into smaller subnets?

Under Split into subnets, set a New prefix longer than the current one. The table lists each subnet's Network, Usable range and Broadcast. It shows only the first 64 subnets when there are more.

What is the wildcard mask and when do I need it?

The Wildcard mask is the inverse of the Subnet mask, for example 0.0.0.255 for /24. It is used in rules such as Cisco ACLs. The tool shows it next to the binary mask and offers Copy all.

Yes. Every tool is free to use, with no account and no credit card. The work runs on your device rather than on our servers, which is what keeps it free to run.

Does it work on mobile?

Yes. It runs in current mobile browsers on iOS and Android, with nothing to install.

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Free Subnet / CIDR Calculator

Calculate network address, broadcast, usable host range, subnet mask, and host count from any IPv4 address and CIDR prefix.

Runs in your browserNo sign-up, no pop-upsNo login requiredFree forever

Works offline once loaded

IPv4 address

Prefix

/0/8/16/24/32

254

Usable hosts

256

Total addresses

Network address

Usable host range

Broadcast address

Subnet mask

Wildcard mask

Mask (binary)

IP class

Address type

Split into subnets

New prefix

2 subnets of /25 with 126 usable hosts each

#	Network	Usable range	Broadcast
1	192.168.1.0/25	192.168.1.1 – 192.168.1.126	192.168.1.127
2	192.168.1.128/25	192.168.1.129 – 192.168.1.254	192.168.1.255

IPv4 subnetting reference. /31 and /32 are handled per RFC 3021 (point-to-point and single-host). All math runs locally in your browser.

Common uses

Subnet Planning for Network AdminsPlan IP allocation, calculate usable hosts, and size subnets for your network.
Subnetting Practice for IT StudentsCheck your subnetting homework and CCNA practice problems instantly.
Home Lab & Self-Hosting SubnetsPlan IP ranges for your home network, VLANs, Docker, and self-hosted services.
Plan Cloud VPC CIDR BlocksSize AWS/GCP/Azure VPC and subnet CIDR ranges before you provision.
CIDR Ranges for Firewall RulesConvert IP ranges to CIDR notation for firewall allow/deny rules and ACLs.

How It Works

All calculations run entirely in your browser using hand-written bitwise arithmetic — no library, no server round-trip. You enter an IPv4 address and CIDR prefix length; the tool applies standard bit-masking operations directly in JavaScript to derive every subnet property instantly as you type.

1
Input parsing and validation
The tool splits the dotted-decimal IP address into four octets, validates each is 0–255, and packs them into a 32-bit unsigned integer using left-shift operations. Invalid addresses are caught before any calculation runs.
2
Bitwise mask construction
From the CIDR prefix length, a 32-bit subnet mask is built by left-shifting 0xFFFFFFFF by (32 − prefix). Bitwise AND with the IP integer yields the network address; bitwise OR with the inverted mask yields the broadcast address. Total host count is computed as 2^(32 − prefix).
3
Class and RFC 1918 detection
The first octet is compared against the class A/B/C/D/E boundary values to assign an IP class. A separate check tests whether the address falls within the 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, or 127.0.0.0/8 private ranges defined in RFC 1918.
4
Subnet splitting and shareable state
The subnet splitter divides the current network into equal child subnets at a chosen longer prefix: it steps through integer offsets of 2^(32 − new prefix) from the base address, computing each child's network, broadcast, and usable range on the fly. The current IP and prefix are written to the URL hash so results can be bookmarked or shared.