CIDR prefix lengths for common subnet masks

Subnet mask CIDR prefix length Subnet mask CIDR prefix length
255.255.0.0 /16 255.255.254.0 /23
255.255.128.0 /17 255.255.255.0 /24
255.255.192.0 /18 255.255.255.128 /25
255.255.224.0 /19 255.255.255.192 /26
255.255.240.0 /20 255.255.255.224 /27
255.255.248.0 /21 255.255.255.240 /28
255.255.252.0 /22 255.255.255.248 /29