CIDR & Subnet Calculator
Enter an IPv4 CIDR block like 10.0.0.0/22 to get the network, broadcast, usable host range, masks and a binary breakdown. Also check whether an IP belongs to a block, and split a block into equal subnets. Everything runs in your browser.
About this tool
All arithmetic is plain 32-bit unsigned math on the IPv4 address space — the same math your router does. A /n prefix means the first n bits identify the network and the remaining 32−n bits identify hosts, giving 2^(32−n) addresses. In a normal subnet the first address (network) and the last (broadcast) are not assignable, so usable hosts = total − 2. /31 is the RFC 3021 point-to-point exception (both addresses usable) and /32 is a single host route.
Cloud VPC sizing hints: AWS VPCs must be between /16 and /28, and AWS reserves 5 addresses per subnet (network, router, DNS, future use, broadcast) — so a /24 subnet gives 251 usable IPs, not 254. GCP reserves 4 addresses per subnet and allows subnets from /29 up. A common starting layout: a /16 VPC (65,536 addresses) split into /20 subnets (4,096 each) per availability zone, keeping spare ranges for growth. Kubernetes clusters are hungry — give pod ranges at least a /18 on GKE-style IP-alias networks.
Your input never leaves the page — there is no server, no upload, and no tracking of tool inputs.
Every prefix length explained
/8 /9 /10 /11 /12 /13 /14 /15 /16 /17 /18 /19 /20 /21 /22 /23 /24 /25 /26 /27 /28 /29 /30 /31 /32