CIDR calculator
Paste a CIDR block to see the range, mask, wildcard and host count.
Runs 100% in your browserHow to read a CIDR block
- Paste a CIDR block. Enter a CIDR like 10.0.0.0/16 or any IP plus a prefix.
- Read the block. Network, broadcast, host range, mask, wildcard and totals appear instantly.
- Copy the summary. Use Copy to grab the block summary as plain text.
About CIDR blocks
CIDR replaced the old class-A/B/C model in 1993, letting you allocate any size of address block
rather than forcing 224, 216 or 28 hosts. A /24
gives 256 addresses, a /22 gives 1,024, and so on — each step of N doubles the
block. Cloud providers use CIDR everywhere: AWS VPCs, GCP networks, Azure VNets, Kubernetes pod
and service ranges. This page solves the common question "what IPs are in this block, and how
many can I actually assign?" without touching a server.
Frequently asked questions
- Classless Inter-Domain Routing (RFC 4632) writes an IP and prefix together as A.B.C.D/N, where N is the number of network bits. 192.168.1.0/24 covers 192.168.1.0–192.168.1.255.
- Same math, framed around the CIDR block itself rather than a specific host. Paste a CIDR and you get its range, mask, hosts and class summary.
- Enter an IP too — the network address is computed from whatever IP you give. To inspect a known CIDR, paste it directly, e.g. 10.0.0.0/16.
- No. Calculations are pure client-side JavaScript with strict CSP — there is no fetch to a server.