Network · Developer

Subnet mask cheat sheet.

All 33 IPv4 prefix lengths, /0 to /32, with the subnet mask, wildcard mask, total addresses and usable hosts. Type a prefix below to highlight its row, or scroll the table.

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Inputs

Result

Enter a prefix length to look it up.

IPv4 CIDR and subnet mask table

CIDRSubnet maskWildcard maskTotal addressesUsable hosts
/00.0.0.0255.255.255.2554,294,967,2964,294,967,294
/1128.0.0.0127.255.255.2552,147,483,6482,147,483,646
/2192.0.0.063.255.255.2551,073,741,8241,073,741,822
/3224.0.0.031.255.255.255536,870,912536,870,910
/4240.0.0.015.255.255.255268,435,456268,435,454
/5248.0.0.07.255.255.255134,217,728134,217,726
/6252.0.0.03.255.255.25567,108,86467,108,862
/7254.0.0.01.255.255.25533,554,43233,554,430
/8255.0.0.00.255.255.25516,777,21616,777,214
/9255.128.0.00.127.255.2558,388,6088,388,606
/10255.192.0.00.63.255.2554,194,3044,194,302
/11255.224.0.00.31.255.2552,097,1522,097,150
/12255.240.0.00.15.255.2551,048,5761,048,574
/13255.248.0.00.7.255.255524,288524,286
/14255.252.0.00.3.255.255262,144262,142
/15255.254.0.00.1.255.255131,072131,070
/16255.255.0.00.0.255.25565,53665,534
/17255.255.128.00.0.127.25532,76832,766
/18255.255.192.00.0.63.25516,38416,382
/19255.255.224.00.0.31.2558,1928,190
/20255.255.240.00.0.15.2554,0964,094
/21255.255.248.00.0.7.2552,0482,046
/22255.255.252.00.0.3.2551,0241,022
/23255.255.254.00.0.1.255512510
/24255.255.255.00.0.0.255256254
/25255.255.255.1280.0.0.127128126
/26255.255.255.1920.0.0.636462
/27255.255.255.2240.0.0.313230
/28255.255.255.2400.0.0.151614
/29255.255.255.2480.0.0.786
/30255.255.255.2520.0.0.342
/31255.255.255.2540.0.0.122
/32255.255.255.2550.0.0.011

Usable hosts are total addresses minus 2 (network and broadcast) for /0 to /30. A /31 has 2 usable addresses under RFC 3021, and a /32 is a single host.

Reading the table

Each step down in prefix length (a larger number) halves the block: /24 has 256 addresses, /25 has 128, /26 has 64, /27 has 32, /28 has 16, /29 has 8 and /30 has 4. The last octet of the mask climbs 0, 128, 192, 224, 240, 248, 252, 254, 255 as the prefix grows by one inside an octet. The wildcard mask is always the inverse of the subnet mask.

To work with a specific address, use the subnet calculator; to convert a single value, use the CIDR to subnet mask converter. The mask and host-count values agree with the variable-length subnet table in RFC 1878, with /31 shown per RFC 3021.

Sources (retrieved 2026-10): RFC 4632 (classless inter-domain routing (CIDR)); RFC 3021 (31-bit prefixes on IPv4 point-to-point links); RFC 1878 (variable length subnet table for IPv4).

Frequently asked questions

How many hosts are in a /24, /25, /26, /27, /28, /29 and /30?

/24 has 254 usable hosts, /25 has 126, /26 has 62, /27 has 30, /28 has 14, /29 has 6 and /30 has 2.

What is the subnet mask for /16?

255.255.0.0, which gives 65,536 addresses and 65,534 usable hosts.

Is a /32 a valid subnet?

Yes. A /32 identifies a single IPv4 address, commonly used as a host route. It has one address and no network or broadcast address.

What is the difference between /31 and /30?

A /30 has 4 addresses and 2 usable hosts. A /31 has 2 addresses and, under RFC 3021, both are usable on a point-to-point link.

Pure arithmetic — no network access

This tool performs standard IPv4 subnet arithmetic entirely in your browser. It does not look anything up, and it doesn't check whether an address or subnet is actually routed, reachable, or assigned to anyone.

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