IP and network calculations
What range does 192.0.2.10/24 cover?
Tools to use
An address copied into an allowlist ends in /24. If you intended only 192.0.2.10, that suffix can select far more than one address. CIDR describes how many leading bits form a common prefix. Expanding it into boundaries is more useful than memorizing suffixes without seeing their effect.
A /24 does not start at the .10 you entered
192.0.2.10/24The network is 192.0.2.0, the endpoint 192.0.2.255, the mask 255.255.255.0, and the total 256 addresses. The entered .10 belongs to the block; it is not its start. Entering .200 with /24 gives the same block. Compare normalized boundaries rather than only input strings.
IPv4 has 32 bits. A /24 fixes the first 24 and leaves eight variable, producing 2⁸=256 combinations. The suffix counts fixed bits, not addresses: increasing it narrows the block. Reversing that relationship can widen an allowlist when you meant to restrict it.
A /25 halves it; a /26 quarters it
192.0.2.10/24 → 192.0.2.0 – 192.0.2.255 (256)
192.0.2.10/25 → 192.0.2.0 – 192.0.2.127 (128)
192.0.2.10/26 → 192.0.2.0 – 192.0.2.63 (64)The other /25 is 192.0.2.128–.255; entering .200/25 selects it. Blocks align to boundaries determined by their size, rather than starting at any address you choose. A range of 128 addresses starting at .10 cannot be represented by simply appending /25; use range-to-CIDR conversion.
If a configuration asks for a mask, /25 corresponds to 255.255.255.128 and /26 to 255.255.255.192. They express the same boundary differently. The calculation does not establish whether a device accepts the setting or whether it conflicts with existing routes.
Separate 256 total addresses from 254 conventional hosts
The conventional IPv4 subnet model reserves the first address for the network and the last for broadcast, leaving 254 of 256 for hosts. A cloud platform may reserve additional addresses. The calculator's 254 is not a guarantee of how many virtual machines a particular service permits.
An allowlist CIDR should not be assumed to omit its first and last addresses just because conventional host capacity is 254. Range membership and assignment policy are separate concepts. CIDR comparison checks ranges; the network's rules determine which addresses can actually be assigned.
Do not subtract two from /31 and /32
192.0.2.10/31 contains .10 and .11. The tool treats both as usable under the RFC 3021 point-to-point model, not as a universal LAN policy. Even if the output field is labeled broadcast, the endpoint is not lost to conventional broadcast reservation in this model.
A /32 selects only 192.0.2.10, for a total of one. At the other extreme, /0 leaves all 32 bits variable and contains 4,294,967,296 addresses. Such an allowlist entry is extremely broad. Check boundaries as well as counts before treating a block as your intended scope.
IPv6 uses 128 bits: /64 is a different scale
Enter 2001:db8::1/64 in IPv6/CIDR. The network is 2001:db8:: and the count is 18,446,744,073,709,551,616: 2⁶⁴ variable combinations. Do not apply IPv4-style last-octet reasoning or subtract two. A range can be calculated without enumerating every address.
The article uses documentation addresses, not reachable destinations. SheepDev does not contact the input, search for unused addresses, or verify ownership. Calculating a range is distinct from being able or authorized to use it.
Choose the next calculation from your question
Use CIDR comparison for membership, subnet splitting for dividing a block, and aggregation for shortening a list without widening coverage. Before changing settings, check each input against its intended range so mistaken assumptions do not propagate.
A host address with a prefix is not a range start
Copying 192.0.2.10/24 does not mean permitting 256 addresses starting at .10. The first 24 bits are fixed, giving .0 through .255; .10 is one member. Use range-to-CIDR conversion when you actually have a start and end. Distinguishing prefix notation from an arbitrary interval helps avoid unintentionally broadening a rule.
192.0.2.10/24 and 192.0.3.10/24 have equal sizes but different locations. Conversely, .10/24 and .200/24 within 192.0.2 represent the same network range. Compare normalized networks as well as raw strings. However, finding the network does not authorize replacing a host-interface address with that network address in a configuration field.
Read the count in context. Total addresses are not necessarily assignable addresses after router or cloud reservations. Even a conventional IPv4 host count omits service-specific reservations. Separate the mathematical statement '256 addresses in this prefix' from the operational claim '254 machines can be placed here,' and check the deployment's allocation rules.