Runs locally in your browser. Nothing you enter is uploaded to our servers.
Result will appear here
Tips for CIDR math
Everything is calculated locally — no network request.
/31 and /32 have special host semantics (point-to-point / single host).
Wildcard masks are useful for some ACL syntaxes.
Double-check prefix length before changing production routes.
IPv6 CIDR is not covered in this calculator yet.
Network math for IPv4 prefixes
Processing stays in your browser — your input is not uploaded to our servers.
CIDR notation like 10.0.0.0/24 is how we write subnet size. The calculator expands prefix, mask, wildcard, and host counts locally.
Use it when writing security groups, routes, or docs — double-check off-by-one on /31 and /32.
Calculate a CIDR block
Enter a prefix
Address plus slash length, for example 192.168.1.0/24.
Read mask and host count
Usable hosts exclude network and broadcast except on /31-/32 special cases.
Copy into the ACL or diagram
Keep the canonical network address, not a random host inside the range, unless you mean that host.
CIDR calculator FAQ
Does this probe the network?
No. It is integer math in the browser. Nothing is scanned.
IPv6?
This helper is IPv4 CIDR. IPv6 prefixes are a different size model.
Why do /31 and /32 look odd?
RFC 3021 uses /31 for point-to-point; /32 is a single host. Host formulas change there.