IP Subnet Calculator
Calculate the network address, broadcast address, subnet mask, wildcard mask, and usable host range from an IPv4 address and CIDR prefix or subnet mask, live in your browser.
🔒 Processed locally in your browser
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How to use
- Type an IPv4 address followed by a CIDR prefix, e.g. 192.168.1.10/24, into the field above.
- You can also use a dotted-decimal subnet mask instead of a prefix, e.g. 192.168.1.10/255.255.255.0.
- Results update instantly below as you type — there's no button to press.
- Use Copy all results to copy every field as plain text, one line per field.
Features
- Supports both CIDR notation (/24) and dotted-decimal subnet masks (255.255.255.0)
- Computes network address, broadcast address, subnet mask, and wildcard mask
- Shows the first and last usable host along with the total and usable host counts
- Correctly handles /31 point-to-point links and /32 single-host addresses
- 100% client-side — your IP addresses never leave your browser
Frequently asked questions
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation writes a subnet as an IP address followed by a slash and a prefix length, like 192.168.1.0/24. The prefix length is the number of leading bits in the subnet mask that are set to 1.
How do I calculate the number of usable hosts?
For prefix lengths /0 through /30, usable hosts = 2^(32 − prefix) − 2, since the first address is reserved for the network and the last for broadcast. /31 conventionally allows both addresses as usable hosts (RFC 3021), and /32 is a single host.
What's the difference between a subnet mask and a wildcard mask?
A subnet mask marks network bits with 1s and host bits with 0s (e.g. 255.255.255.0). A wildcard mask is its bitwise inverse (e.g. 0.0.0.255) and is commonly used in access control list configurations.
Why don't /31 and /32 subnets have a separate usable-host count?
A /32 identifies a single host, so the network, broadcast, and host address are all the same. A /31 has only two addresses and no room for a distinct network/broadcast pair, so RFC 3021 allows both to be used as host addresses on point-to-point links.
Does this tool send my IP address anywhere?
No. All calculations run locally in your browser using plain JavaScript arithmetic. Nothing is sent to a server or stored.