Subnet Mask Cheat Sheet
A complete CIDR subnet cheat sheet mapping /0–/32 prefixes to subnet masks, wildcard masks, and usable host counts. Filter instantly. Free reference, private.
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Every prefix, mask and host count in one table
Subnetting is quick once you have the reference in front of you and slow when you are deriving it each time. This cheat sheet maps every CIDR prefix from /0 to /32 to its subnet mask, wildcard mask and usable host count, so the answer you need is a glance away rather than a calculation.
Why the numbers move the way they do
The table makes the pattern visible. Each step down in prefix doubles the host count and shifts the mask by one bit: a /24 gives 254 usable hosts with a 255.255.255.0 mask, a /23 gives 510, a /25 gives 126. The wildcard mask, which some access lists use, is simply the inverse of the subnet mask. Seeing all three columns together turns three separate mental conversions into one lookup.
A reference you will keep coming back to
Network engineers, whether studying for a certification or configuring a router, reach for this mapping constantly. Having it as a complete, correct table removes the small friction of recomputing a mask under pressure. The reference is static and runs entirely in your browser.
Related tools
- Port Scanner — Check which common ports respond on a host and understand what each exposed service means. Scan only systems you are authorised to test.
- DNS Misconfiguration — Analyze DNS records (TXT, SPF) for security gaps.
- TLS Compat Tester — Check client-server compatibility for TLS versions.
- Firewall Rule Risk — Evaluate firewall rules for over-permissive exposure.
Frequently Asked Questions
What is a wildcard mask?
The bitwise inverse of a subnet mask, used by some access control lists and routing configurations. Where the subnet mask has ones the wildcard has zeros, and vice versa.
How many usable hosts are in a /26?
A /26 spans 64 addresses, of which 62 are usable once the network and broadcast addresses are reserved.
Why does each smaller prefix double the hosts?
Because the prefix length counts fixed network bits; reducing it by one frees an extra host bit, doubling the number of addresses the block covers.
What is the mask for a /30?
255.255.255.252, which leaves two usable hosts, the size commonly used for point-to-point links.
Do I need an internet connection?
No. The cheat sheet is a static reference that runs entirely in your browser.
Privacy & Security
All processing happens locally in your browser — nothing is uploaded.
How to Use
Browse the full CIDR table or type to filter by prefix, mask or host count.
Disclaimer: This tool is provided "as is" without warranty of any kind. Results are for educational and utility purposes.
Related Tools
Port Scanner
NetworkCheck which common ports respond on a host and understand what each exposed service means. Scan only systems you are authorised to test.
DNS Misconfiguration
NetworkAnalyze DNS records (TXT, SPF) for security gaps.
TLS Compat Tester
NetworkCheck client-server compatibility for TLS versions.