The fast subnet calculator for engineers
Enter an IP and prefix to get the network, broadcast, usable range, mask, wildcard, and binary, instantly. No page reload, no sign up, nothing uploaded.
Accepts CIDR (192.0.2.0/24), IP + mask (192.0.2.0 255.255.255.0), or a bare IP (defaults to /24).
11000000.00000000.00000010.0000000011111111.11111111.11111111.00000000Networking calculators
All toolsCIDR calculator
Expand a CIDR block into its full address range and host count.
Subnet mask calculator
Convert between prefix length and subnet mask, both directions.
Wildcard mask calculator
Turn a subnet mask into the wildcard mask used in Cisco ACLs.
Supernet calculator
Summarize multiple networks into one aggregate CIDR route.
IPv6 subnet calculator
Expand, compress, and subnet any IPv6 prefix.
IP converter
Convert an IP between decimal, integer, binary, hex and octal.
MAC address formatter
Reformat a MAC address between colon, dash, dotted and bare forms.
Random IP generator
Generate random valid IPv4 addresses, public or private, for testing.
Reference
CIDR cheat sheetCIDR cheat sheet
Every prefix from /0 to /32 with its mask, wildcard, and host count.
Port numbers
Common TCP and UDP ports, what they do, and their security notes.
Subnet by host count
Need room for N hosts? Find the smallest block that fits.
What is a subnet?
A plain-English guide to subnetting, masks, and CIDR.
Free JSON API
Keyless CIDR and port lookups you can build on. No rate limits.
Why SubnetKit
Most subnet calculators reload the page when you submit, bury the result under ads, or hide the binary and wildcard behind a tab. SubnetKit shows everything at once and recomputes on every keystroke. It is built for people who reach for a subnet calculator ten times a day and want it to get out of the way.
Because all the maths is plain JavaScript running in your browser, nothing you type is ever sent to a server. That also makes it fast: there is no round trip, so results appear the instant you type. Pair it with the CIDR reference for the full prefix table, or the IPv6 subnet calculator when you move to IPv6.
Frequently asked questions
What does a subnet calculator do?
It takes an IP address and a prefix or mask, then works out the network address, broadcast address, usable host range, host count, subnet mask, wildcard mask, and binary form. SubnetKit does all of this instantly in your browser.
Is SubnetKit free?
Yes. Every calculator and reference page is free with no sign up and no limits. Nothing you type is uploaded, because the maths runs entirely on your device.
How do I calculate a subnet?
Enter the IP with its prefix, such as 192.0.2.0/24, or an IP with a dotted mask. The calculator reads off the network, first and last usable host, broadcast, and total addresses as you type.
What is the usable host range?
It is every address in the block except the network address (first) and the broadcast address (last). A /24 has 254 usable hosts; a /30 has 2. A /31 and /32 are special cases handled per RFC 3021.