Enter a start and an end IPv4 address to get the total count, the exact list of CIDR blocks covering the range, and the smallest single CIDR that contains it.
The calculator converts both addresses to numbers, counts the addresses between them inclusive, and then covers the range exactly: starting at the first address it repeatedly takes the largest CIDR block that both aligns at that address and fits in what remains, which yields the shortest possible list of blocks. It also reports the single smallest CIDR that contains the whole range, found from the first bit where the start and end addresses differ — that covering block usually includes addresses outside the range, which the difference between its size and the range count shows.
Why does one range need several CIDR blocks? A CIDR block must start on an address aligned to its size and has a power-of-two length. An arbitrary range such as .10 to .60 lines up with neither rule, so several aligned blocks of different sizes are needed to cover it exactly.
What is the smallest covering CIDR? It is the one CIDR block that contains both the start and the end address. It is convenient for a single route or firewall rule, but it typically also covers addresses outside the requested range.
Can the range span different networks? Yes. Any start and end IPv4 addresses work, including ranges crossing octet boundaries, as long as the end is not lower than the start.