Subnet Calculator
CIDR to mask, range, hosts and class — instant IPv4 math
CIDR in one minute
An IPv4 address is 32 bits; CIDR notation splits them into a network part and a host part with one number. /24 means 24 network bits: 256 addresses where the first names the network, the last broadcasts, and 254 take hosts. Bigger prefix, smaller subnet — /30 leaves just 2 usable addresses, the classic point-to-point link.
What this tool does
- 🌐 Parses CIDR (192.168.1.0/24) or IP + mask input
- 📋 Reports mask, wildcard, network, broadcast and usable range
- 🔢 Counts usable hosts with /31 and /32 handled correctly
- 🏷️ Names the address class and flags private ranges
When to use it
- Sizing subnets for VLANs or cloud VPCs
- Checking whether two hosts share a subnet
- Studying for a networking exam
Privacy: pure arithmetic in your browser — IP addresses you type never leave your device.
Last updated · 2026-09-01
How the math works
Addresses become unsigned 32-bit integers; the mask is 32-bits-minus-prefix ones. Network = IP AND mask, broadcast = network OR NOT mask, usable range excludes both ends except at /31 and /32. Private ranges follow RFC 1918 plus loopback and link-local.
Why subnet here?
Two input styles, zero friction
Paste CIDR or type an IP plus a dotted mask — both parse to the same full table, with clear errors instead of silent wrong math on bad input.
Edge cases done right
/31 point-to-point links (2 usable, no reservation) and /32 host routes (1 address) follow the RFCs instead of the naive minus-two every calculator cargo-cults.
Answers, not just numbers
Class, private-range verdict and wildcard mask ride along with the raw table, so firewall rules and documentation write themselves.
Frequently asked questions
What does /24 actually mean?⌄
The number after the slash counts network bits: /24 fixes the first 24 of 32 bits (mask 255.255.255.0), leaving 8 host bits — 256 addresses, 254 usable after reserving network and broadcast.
Why are network and broadcast unusable?⌄
By convention the all-zeros address names the subnet itself and the all-ones address broadcasts to everyone on it — hosts can't claim either, hence total minus two (except /31 and /32, handled explicitly).
Does it support IPv6?⌄
No — IPv6 subnetting (with 128-bit space and no broadcast concept) is a different tool. This one is exact IPv4 CIDR math only.
Frequently asked questions
What does /24 actually mean?
The number after the slash counts network bits: /24 fixes the first 24 of 32 bits (mask 255.255.255.0), leaving 8 host bits — 256 addresses, 254 usable after reserving network and broadcast.
Why are network and broadcast unusable?
By convention the all-zeros address names the subnet itself and the all-ones address broadcasts to everyone on it — hosts can't claim either, hence total minus two (except /31 and /32, handled explicitly).
Does it support IPv6?
No — IPv6 subnetting (with 128-bit space and no broadcast concept) is a different tool. This one is exact IPv4 CIDR math only.
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