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Subnet Mask Cheat Sheet (/0–/32)

Every IPv4 prefix length with its dotted-decimal mask, wildcard, total address count and usable host count. Print it, pin it, or link straight to any row.

IPv4 subnet masks by prefix length
Prefix (CIDR)Subnet maskWildcard maskTotal addressesUsable hosts
/0 0.0.0.0 255.255.255.255 4,294,967,296 4,294,967,294
/1 128.0.0.0 127.255.255.255 2,147,483,648 2,147,483,646
/2 192.0.0.0 63.255.255.255 1,073,741,824 1,073,741,822
/3 224.0.0.0 31.255.255.255 536,870,912 536,870,910
/4 240.0.0.0 15.255.255.255 268,435,456 268,435,454
/5 248.0.0.0 7.255.255.255 134,217,728 134,217,726
/6 252.0.0.0 3.255.255.255 67,108,864 67,108,862
/7 254.0.0.0 1.255.255.255 33,554,432 33,554,430
/8 255.0.0.0 0.255.255.255 16,777,216 16,777,214
/9 255.128.0.0 0.127.255.255 8,388,608 8,388,606
/10 255.192.0.0 0.63.255.255 4,194,304 4,194,302
/11 255.224.0.0 0.31.255.255 2,097,152 2,097,150
/12 255.240.0.0 0.15.255.255 1,048,576 1,048,574
/13 255.248.0.0 0.7.255.255 524,288 524,286
/14 255.252.0.0 0.3.255.255 262,144 262,142
/15 255.254.0.0 0.1.255.255 131,072 131,070
/16 255.255.0.0 0.0.255.255 65,536 65,534
/17 255.255.128.0 0.0.127.255 32,768 32,766
/18 255.255.192.0 0.0.63.255 16,384 16,382
/19 255.255.224.0 0.0.31.255 8,192 8,190
/20 255.255.240.0 0.0.15.255 4,096 4,094
/21 255.255.248.0 0.0.7.255 2,048 2,046
/22 255.255.252.0 0.0.3.255 1,024 1,022
/23 255.255.254.0 0.0.1.255 512 510
/24 255.255.255.0 0.0.0.255 256 254
/25 255.255.255.128 0.0.0.127 128 126
/26 255.255.255.192 0.0.0.63 64 62
/27 255.255.255.224 0.0.0.31 32 30
/28 255.255.255.240 0.0.0.15 16 14
/29 255.255.255.248 0.0.0.7 8 6
/30 255.255.255.252 0.0.0.3 4 2
/31 255.255.255.254 0.0.0.1 2 2 †
/32 255.255.255.255 0.0.0.0 1 1 ‡

Special cases

† /31 — Under RFC 3021 a two-address /31 is usable as a point-to-point link: both addresses are assigned (one per router), so there are 2 usable hosts instead of the traditional total − 2 = 0.

‡ /32 — A /32 is a single-address host route. It has no network or broadcast split and counts exactly 1 usable address. Common for loopbacks and device-specific routes.

For every other prefix the traditional rule applies: the first address identifies the network, the last is the broadcast address, leaving total − 2 usable host addresses.

Using this table