Enter any IPv4 address with a CIDR prefix to get the network address, broadcast, usable host range, masks and binary breakdown — calculated instantly and privately in your browser. 🌐
IPv4 / CIDR
🔒 All subnet math runs in your browser — the address you type is never sent anywhere.
Pure integer math, no rounding — every value from /0 to /32 including the /31 and /32 special cases.
Binary view of the IP and mask makes CIDR finally click — perfect for CCNA, Network+ and homework.
Your internal network addresses never leave your browser — nothing is logged or transmitted.
CIDR (Classless Inter-Domain Routing) notation describes a network as an IP address plus a prefix length — 192.168.1.0/24 means the first 24 bits identify the network and the remaining 8 bits identify hosts. The prefix maps directly to a subnet mask: /24 is 255.255.255.0, /16 is 255.255.0.0, /26 is 255.255.255.192. The wildcard mask is simply the inverse (0.0.0.255 for /24) and is what Cisco ACLs and OSPF configuration expect.
Every subnet reserves two addresses: the all-zeros network address and the all-ones broadcast address. That is why a /24 offers 2^8 − 2 = 254 usable hosts and a /30 only 2. Two modern exceptions matter in 2026 networks: a /31 (RFC 3021) provides 2 usable addresses for point-to-point router links with no broadcast, and a /32 identifies a single host — the standard form for firewall rules, loopbacks and route advertisements.
The calculator also identifies the historical class (A: 1–126, B: 128–191, C: 192–223, D multicast, E experimental) and whether the address is private or public. The RFC 1918 private ranges — 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 — are what your home router, office LAN and cloud VPCs use internally; they are never routed on the public internet. It also flags loopback (127/8), link-local/APIPA (169.254/16) and carrier-grade NAT (100.64/10) space, so you can tell at a glance why a device got a weird address.
Whether you are carving an AWS or Azure VPC into subnets, sizing a VLAN, studying for the CCNA, or just figuring out which addresses are free on your home network, all of the math here is exact 32-bit integer arithmetic done locally in your browser.
Subnetting divides an IP address into a network portion and a host portion, with CIDR notation stating how many leading bits belong to the network. A /24 reserves 24 bits for the network and leaves 8 for hosts. Two addresses in every subnet are unusable: the all-zeros address identifies the network itself and the all-ones address is the broadcast, which is why a /24 offers 254 usable hosts rather than 256. Each additional network bit halves the host count, so subnet sizes move in powers of two and there is no way to create a subnet of, say, exactly 100 addresses.
Total addresses = 2^(32 − prefix)Usable hosts = 2^(32 − prefix) − 2Subnet mask = prefix ones followed by (32 − prefix) zerosSubnets created = 2^(new prefix − old prefix)where:
Assumptions: IPv4 with the standard two reserved addresses. Point-to-point /31 links are a defined exception under RFC 3021. IPv6 does not reserve a broadcast address and uses vastly larger prefixes.
SourceRFC 3021
Divide a standard home-sized network into four equal subnets.
ResultFour /26 subnets of 62 usable hosts each — mask 255.255.255.192
The first subnet runs .1 to .62 with .63 as its broadcast; the second starts at .65. Needing 100 hosts would force a /25 (126 hosts) because subnet sizes only come in powers of two — there is no intermediate option.
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