--- title: CIDR Calculator – Ranges, Masks & Host Counts description: Free CIDR calculator. Enter a block like 10.0.0.0/22 and get the network and broadcast address, first and last usable host, subnet and wildcard masks and the host count — then split it into smaller prefixes for planning. Instant, no signup. canonical: https://watchfor.io/cidr-calculator --- [Back to all free tools](/free-tools) # CIDR Calculator Turn CIDR notation into what it actually covers — network and broadcast address, first and last usable host, subnet and wildcard mask, host count — and split a block into smaller prefixes for planning. Paste 10.0.0.0/22 and see the whole picture. Free, instant, no signup. CIDR notation packs a whole address block into one number after the slash: 10.0.0.0/22 is 1,024 addresses, /24 is 256, /30 is four. The notation is compact and the mental arithmetic is not — which addresses are in the block, which one is the broadcast, how many hosts fit, and what the mask looks like in dotted form for the firewall that won't take a prefix length. Paste any address with a prefix (or an address and a mask) and this calculator lays all of it out: network and broadcast, first and last usable host, subnet and wildcard masks, the address class and whether it's private, public or CGNAT space. Advanced mode adds the binary breakdown and a splitter for carving a block into equal subnets. IP address or paste CIDR Prefix subnet mask Mode Simple Advanced 192.168.1.0/24 254 usable hosts · 192.168.1.1 – 192.168.1.254 Private (RFC 1918) Results Copy all results Network address 192.168.1.0 Broadcast address 192.168.1.255 Usable host range 192.168.1.1 – 192.168.1.254 Subnet mask 255.255.255.0 Wildcard mask 0.0.0.255 Addresses 256 total · 254 usable ## How to use the Subnet Calculator - Enter an IP address — or paste a full CIDR like 10.0.0.0/8 ; the prefix moves into the selector automatically. - Pick the prefix — every option shows its dotted mask ( /24 — 255.255.255.0 ), so you never translate in your head. - Read the results instantly — network, broadcast, usable range, mask and wildcard. Click any value to copy it. Use ‹ › to step to the neighbouring subnet. - Switch to Advanced for the binary breakdown with colored network/host bits, IP properties (class, hex, PTR record), and a subnet splitter that plans a block into equal smaller subnets. ## What is a subnet and CIDR notation? A subnet is a slice of IP address space that shares one network prefix. CIDR notation describes it as an address plus a prefix length — 192.168.1.0/24 means "the first 24 bits identify the network, the remaining 8 bits number the hosts". Those 8 host bits give 256 addresses, of which two are reserved: the lowest (the network address ) and the highest (the broadcast address ) — leaving 254 usable hosts. Two edge cases are worth knowing. A /31 has no room for those two reserved addresses, so RFC 3021 allows both addresses to be used on point-to-point links. A /32 is a single host — the form you'll see in firewall rules and route tables. ## Common subnet sizes cheat sheet CIDR Subnet mask Usable hosts Typical use /8 255.0.0.0 16,777,214 Whole private 10.x space /16 255.255.0.0 65,534 Large site or VPC /24 255.255.255.0 254 The classic LAN /26 255.255.255.192 62 Department / VLAN /28 255.255.255.240 14 Small server segment /30 255.255.255.252 2 Router links (legacy) /31 255.255.255.254 2 Point-to-point (RFC 3021) /32 255.255.255.255 1 Single host / firewall rule Working with IPv6? The [IPv6 subnet calculator](/ipv6-subnet-calculator) does the 128-bit version — compression, prefix ranges and /48-to-/64 planning. Planning address space for real infrastructure? Pair the calculator with our [What Is My IP](/whats-my-ip) tool to see your current address, and [ping](/ping-test) or [port-check](/port-checker) the hosts you carve out. ## Frequently asked questions What does the number after the slash mean? The prefix length — how many leading bits of the address are the network part. /24 means 24 network bits and 8 host bits, so 2⁸ = 256 addresses. Each step down the prefix (/23, /22…) doubles the block. How many usable hosts are in a /24, /26, /30? Subtract the network and broadcast address: /24 → 254, /25 → 126, /26 → 62, /27 → 30, /28 → 14, /29 → 6, /30 → 2. A /31 is the point-to-point exception (2 usable, RFC 3021) and a /32 is a single host. Is 10.0.0.0/8 the same as 10.0.0.0 255.0.0.0? Yes. The prefix length and the dotted-decimal mask say the same thing: /8 is 255.0.0.0, /16 is 255.255.0.0, /24 is 255.255.255.0. The wildcard mask (used in Cisco ACLs) is the inverse — 0.0.0.255 for a /24. Which ranges are private? 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 (RFC 1918). 100.64.0.0/10 is carrier-grade NAT space, 169.254.0.0/16 is link-local, 127.0.0.0/8 is loopback. The calculator labels the range you enter. How do I split a /22 into /24s? A /22 holds four /24s: 10.0.0.0/24, 10.0.1.0/24, 10.0.2.0/24 and 10.0.3.0/24. Enter the /22 and use the subnet splitter in advanced mode to list them — it works for any target prefix, not just /24. Does this work for IPv6? This page is IPv4. IPv6 blocks (a /64, a /48, ip6.arpa names, address compression) are handled by the IPv6 subnet calculator, linked in the related tools below. ## The subnet is planned — now watch what lives in it WatchFor monitors the hosts and services behind these addresses — ping, TCP ports, HTTP, DNS and 20+ more check types from multiple regions, with confirmed alerts when something drops. [Start monitoring for free](/pricing) Free plan · 15 monitors · no credit card required --- Canonical page: https://watchfor.io/cidr-calculator · Site guide: https://watchfor.io/llms.txt