Netmask Quick Reference # bits # hosts Usable hosts netmask /4 268435456 268435454 240.0.0.0 /5 134217728 134217726 248.0.0.0 /6 67108864 67108862 252.0.0.0 /7 33554432 33554430 254.0.0.0 /8 16777216 16777214 255.0.0.0 class A network /9 8388608 8388606 255.128.0.0 /10 4194304 4194302 255.192.0.0 /11 2097152 2097150 255.224.0.0 /12 1048576 1048574 255.240.0.0 /13 524288 524286 255.248.0.0 /14 262144 262142 255.252.0.0 /15 131072 131070 255.254.0.0 /16 65536 65534 255.255.0.0 class B network /17 32768 32766 255.255.128.0 /18 16384 16382 255.255.192.0 /19 8192 8190 255.255.224.0 /20 4096 4094 255.255.240.0 /21 2048 2046 255.255.248.0 /22 1024 1022 255.255.252.0 /23 512 510 255.255.254.0 /24 256 254 255.255.255.0 class C network /25 128 126 255.255.255.128 /26 64 62 255.255.255.192 /27 32 31 255.255.255.224 /28 16 14 255.255.255.240 /29 8 6 255.255.255.248 /30 4 2 255.255.255.252 /31 point to point links only /32 1 1 255.255.255.255 single IP address
