How do I use the IP subnet calculator (CIDR)?
- Enter an IP address and prefix length in CIDR notation.
- Press Calculate subnet.
- Use the range and masks in your router, firewall or cloud network settings.
IP subnet calculator (CIDR): frequently asked questions
What does /24 mean?
The first 24 bits are the network part, leaving 8 bits for hosts: 256 addresses, 254 usable.
Why are two addresses not usable?
The first address identifies the network and the last is the broadcast address. /31 and /32 are special cases.
What is a wildcard mask?
The inverse of the subnet mask, used in Cisco ACLs and some firewall rules.
What are the private IP ranges?
10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 (RFC 1918).
Does it support IPv6?
Not yet; IPv6 support is planned.
How many hosts in a /26?
64 addresses, 62 usable.
Can I use it for cloud VPCs?
Yes. Note that AWS, Azure and Google Cloud reserve a few extra addresses in each subnet.
Is anything sent to a server?
No. It runs in your browser.
Why do results differ from another checker?
DNS and web responses are cached for their TTL and may differ by location. Our checks use Cloudflare’s 1.1.1.1 resolver.
Is the ip subnet calculator (cidr) free?
Yes. It is free with no sign-up and no usage limits for normal use.