ipv4 subnets
CIDR | Addresses | Netmask | Size | Comment ---- | ------------- | --------------- | --------------- | ------- /32 | 1 | 255.255.255.255 | 1/256 of /24 | A single host /31 | 2 | 255.255.255.254 | 1/128 of /24 | 0 usable addresses /30 | 4 | 255.255.255.252 | 1/64 of /24 | /29 | 8 | 255.255.255.248 | 1/32 of /24 | /28 | 16 | 255.255.255.240 | 1/16 of /24 | /27 | 32 | 255.255.255.224 | 1/8 of /24 | /26 | 64 | 255.255.255.192 | 1/4 of /24 | /25 | 128 | 255.255.255.128 | 1/2 of /24 | /24 | 256 | 255.255.255.0 | 1 x /24 | Class C /23 | 512 | 255.255.254.0 | 2 x /24 | /22 | 1.024 | 255.255.252.0 | 4 x /24 | /21 | 2.048 | 255.255.248.0 | 8 x /24 | /20 | 4.096 | 255.255.240.0 | 16 x /24 | /19 | 8.192 | 255.255.224.0 | 32 x /24 | /18 | 16.384 | 255.255.192.0 | 64 x /24 | /17 | 32.768 | 255.255.128.0 | 128 x /24 | /16 | 65.536 | 255.255.0.0 | 256 x /24 | Class B /15 | 131.072 | 255.254.0.0 | 2 x /16 | /14 | 262.144 | 255.252.0.0 | 4 x /16 | /13 | 524.288 | 255.248.0.0 | 8 x /16 | /12 | 1.048.576 | 255.240.0.0 | 16 x /16 | /11 | 2.097.152 | 255.224.0.0 | 32 x /16 | /10 | 4.194.304 | 255.192.0.0 | 64 x /16 | /9 | 8.388.608 | 255.128.0.0 | 128 x /16 | /8 | 16.777.216 | 255.0.0.0 | 256 x /16 | Class A /7 | 33.554.432 | 254.0.0.0 | 2 x /8 | /6 | 67.108.864 | 252.0.0.0 | 4 x /8 | /5 | 268.435.456 | 248.0.0.0 | 8 x /8 | /4 | 268.435.456 | 240.0.0.0 | 16 x /8 | /3 | 536.870.912 | 224.0.0.0 | 32 x /8 | /2 | 1.073.741.824 | 192.0.0.0 | 64 x /8 | /1 | 2.147.483.648 | 128.0.0.0 | 128 x /8 | /0 | 4.294.967.296 | 0.0.0.0 | 256 x /8 |
Amount of **usable addresses** in a subnet, is 2 less than total addresses.
IETF RFC1878: Variable Length Subnet Table For IPv4