CIDR Calculator
Convert a CIDR block to its IP range and total addresses, or find the smallest CIDR covering a range.
IP range: 10.0.0.0 – 10.255.255.255
Total addresses: 16,777,216
Range to covering CIDR
Smallest covering CIDR:0.0.0.0/0
Turn a CIDR block into its address range, or work out the smallest prefix that covers two IP addresses.
How to use
- Enter a CIDR block such as 10.0.0.0/8.
- Read the first/last address and total count.
- Or enter a start and end IP to get the smallest covering prefix.
Frequently asked questions
- What does /24 mean?
- The number after the slash is how many leading bits are fixed for the network. /24 fixes 24 bits, leaving 8 host bits and 256 addresses.
- Why does the covering CIDR include extra addresses?
- A single CIDR block is always a power of two aligned to its boundary, so the smallest block that fully contains an arbitrary range may be larger than the range itself.