CIDR Calculator
Enter an IP address and prefix length or subnet mask to instantly calculate subnet details.
Last updated: May 29, 2026
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Buy me a coffeeWhat is CIDR Calculator?
CIDR Calculator computes all subnet information from a CIDR (Classless Inter-Domain Routing) notation. Given an IPv4 address and either a prefix length (/24) or dotted subnet mask (255.255.255.0), it calculates the network address, broadcast address, first and last usable host, number of usable hosts, wildcard mask, and binary representations. Supports all prefix lengths from /0 to /32.
How to Use CIDR Calculator
Enter an IPv4 address.
Enter a prefix length (e.g. 24) or subnet mask (e.g. 255.255.255.0).
Results appear instantly.
Common Use Cases
- Planning IP address allocation for a network segment.
- Verifying subnet boundaries when configuring firewalls or routers.
- Learning subnetting and CIDR notation for networking certifications.
- Checking how many hosts fit in a given subnet before provisioning.
Example Input and Output
CIDR /24 calculation for 192.168.1.0.
IP: 192.168.1.0
Prefix: /24Network: 192.168.1.0
Broadcast: 192.168.1.255
Hosts: 192.168.1.1 – 192.168.1.254
Usable: 254Privacy
All calculations run locally in the browser.
Frequently Asked Questions
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation expresses a network as an IP address followed by a slash and prefix length (e.g. 192.168.1.0/24). The prefix length indicates how many bits are in the network portion of the address.
Can I enter a subnet mask instead of a prefix?
Yes. Enter the subnet mask in dotted-decimal format (e.g. 255.255.255.0) in the Prefix field. The calculator converts it to a prefix length automatically.
What are /31 and /32 subnets?
/32 is a host route (single IP, no broadcast). /31 is a point-to-point link (2 addresses, both usable per RFC 3021).
Is my data uploaded?
No. All calculation runs in your browser.
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