One address. One prefix. The complete block.
Make the CIDR
boundary visible.
Paste an IPv4 address and prefix. See which bits name its block, where the numerical range starts and ends, and how many addresses it contains.
Enter an address / prefix
Count addresses, not deployable hosts
The inclusive count includes every numerical address in the block. It does not subtract endpoints or determine whether an address is usable on a particular network.
Read the /31 and /32 boundary explanationInspect the exact result
Canonical block
- Lowest numerical address
- Highest numerical address
- Full address count
- Entered-address offset (zero based)
- Prefix mask
- Inverse wildcard
- Entered address
- Prefix / remainder bits
- /
Where the bits go
Prefix bits stay. Remainder bits become zero in the canonical lower address. Four rows of eight bits are used on narrow screens.
Entered address
Canonical lower address
Prefix mask
Keep the entered address and its block separate
A host address need not equal the first address of its CIDR block. The result explicitly shows both, so the canonical prefix does not silently replace what you entered. This is a local numerical explanation: it does not contact, scan or classify the address.
Understand the calculation or check original worked examples, including the full /0 range and the one-address /32 case.