Subnet Calculator — IPv4, CIDR & Mask
Free IPv4 subnet calculator — network & broadcast address, host ranges, wildcard mask, binary breakdown, subnet splitting. Exact 32-bit math.
Each octet 0–255. Tip: paste a full 10.0.0.0/8 here.
Enter a full IPv4 address to test membership.
× networks · usable hosts each
🔒 100% in-browser, zero network calls — every value is exact 32-bit math. Handles /31 (RFC 3021, 2 usable) and /32 edge cases correctly. Where LLMs routinely fumble subnet boundaries and host counts, this is deterministic and instant.
Why you’ll love Subnet Calculator — IPv4, CIDR & Mask
Instant & free
No signup, no paywall, no limits — Subnet Calculator — IPv4, CIDR & Mask works the moment the page loads.
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Everything runs in your browser. Nothing you enter is ever uploaded or stored on a server.
Works on any device
Fully responsive and touch-friendly — use it on your phone, tablet or desktop.
Built by developers
Accurate, fast and keyboard-friendly — the details developers care about.
How to use it
Open it
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Get your result
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About Subnet Calculator — IPv4, CIDR & Mask
This IPv4 subnet calculator does exact 32-bit binary math in your browser — no server calls, no sign-up, and results appear as you type. Enter an address (or paste a full CIDR like 10.0.0.0/8 into the first octet and it fills everything), pick a prefix with the slider, number box or mask dropdown, and you instantly get the network address, broadcast address, first and last usable host, subnet mask, wildcard mask, and total versus usable address counts.
The method is the same one routers use: the network address is the IP ANDed with the subnet mask, and the broadcast address is the network ORed with the wildcard (inverted) mask. A colour-coded binary breakdown shows exactly which bits are network and which are host, which is the fastest way to actually understand subnetting rather than memorise it. Worked example: 192.168.1.130/26 has mask 255.255.255.192, network 192.168.1.128, broadcast 192.168.1.191, and 62 usable hosts (2^6 − 2) from .129 to .190.
Three extra tools cover the questions that follow: a membership tester tells you whether any IP falls inside the current network, a splitter divides the block into 2–64 equal subnets with each new CIDR, range and broadcast listed, and a host planner finds the smallest prefix that fits N hosts. It also identifies the address class (A–E) and type — RFC 1918 private, public, loopback, APIPA link-local, CGNAT (100.64/10) or multicast — and handles the /31 and /32 edge cases correctly, where many calculators (and most AI chatbots) get host counts wrong.
Popular uses
Frequently asked questions
A /p prefix means the first p bits are the network portion. Bitwise-AND the IP with the subnet mask to get the network address, then OR the network with the wildcard mask (the mask inverted) to get the broadcast. For 172.16.5.9/20 the mask is 255.255.240.0, so the network is 172.16.0.0 and the broadcast is 172.16.15.255. The binary breakdown panel shows this bit by bit.
The classic formula 2^(host bits) − 2 reserves one address for the network and one for broadcast, which would leave /31 and /32 with none. RFC 3021 changed that for /31: on point-to-point links both addresses are usable, and it is now standard practice on router-to-router links. A /32 is a host route — a single address, commonly used in loopbacks, BGP peering and firewall rules. This calculator applies both rules, which many tools miss.
It is the bitwise inverse of the subnet mask — 255.255.255.0 becomes 0.0.0.255. Cisco IOS uses wildcard masks instead of subnet masks in ACLs and OSPF network statements, so having it computed alongside the mask saves a mental inversion step (and a classic exam mistake).
AND the candidate IP with the subnet mask; if the result equals the network address, it is inside. The "Does this network contain an IP?" panel does this for you and also shows the usable range, which is handy for verifying firewall allowlists, VPC route tables or DHCP scopes without doing binary by hand.
It is IPv4-only, and the splitter divides a block into equal power-of-two subnets (2 to 64). For unequal allocations, use the "smallest subnet for N hosts" planner per requirement, largest first, and assign each block sequentially from the parent network — the planner tells you the prefix and how many such subnets your block yields.
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