Tool
Make sense of any subnet.
Type a CIDR block, 10.0.0.0/22, 192.168.1.0/24, and see exactly what it covers: the network and broadcast addresses, the usable host range, the mask, and a map of the address space you can split, in your browser.
Network address in binary, the green bits are the network prefix, the rest is host space.
Split into equal subnets
How CIDR works
An IPv4 address is 32 bits. The /N in a CIDR block says the first N bits are fixed, the network prefix, and the remaining 32−N bits are free to number hosts. So a /24 fixes 24 bits and leaves 8 for hosts: 256 addresses, of which the first is the network address and the last is the broadcast, leaving 254 usable. Each step up in prefix length halves the block; each step down doubles it. Splitting a network into subnets just means borrowing host bits to become network bits.