CIDR / Subnet Calculator
Parses an IPv4 CIDR block and shows the network address, broadcast address, subnet and wildcard masks, usable host range and address type. Every calculation runs in your browser.
Results
Enter a CIDR block and press "Calculate".
Enter a valid IPv4 CIDR block — e.g. 192.168.1.0/24.
- Prefix length
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- Broadcast address
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- Subnet mask
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- Wildcard mask
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- First usable host
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- Last usable host
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- Usable hosts
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- Total addresses
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- IP class
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- Address type
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Frequently Asked Questions
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation writes an IP address followed by a slash and a prefix length — e.g. 10.0.0.0/16. The prefix says how many bits form the network part of the address; the remaining bits are host addresses.
Why is the usable host count two fewer than the total addresses?
In every subnet the first address is the network address and the last is the broadcast address; neither is assigned to a host. So usable hosts = total − 2. Two exceptions: a /31 defines 2 usable addresses for point-to-point links (RFC 3021), and a /32 represents a single host.
Which IP ranges are private?
RFC 1918 defines three private ranges: 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. These addresses are not routed on the internet; they are used on local networks and behind NAT. Additionally 127.0.0.0/8 is loopback and 169.254.0.0/16 is link-local.
What are the Pod CIDR and Service CIDR in Kubernetes?
A Kubernetes cluster assigns pod IPs from one CIDR block (the pod network CIDR, e.g. 10.244.0.0/16) and Service IPs from a separate block (the service CIDR, e.g. 10.96.0.0/12). The two blocks must not overlap with each other or with the node network — an overlap causes routing failures.
How many addresses do /24, /16 and /8 hold?
A /24 holds 256 addresses (254 usable hosts), a /16 holds 65,536 addresses (65,534 hosts), and a /8 holds 16,777,216 addresses. The address count is 2^(32 − prefix) — each bit shorter doubles the block.