Traditional subnets
The network and broadcast addresses are reserved. Usable addresses fall between them.
Address analysis
IPv4 Subnet Calculator
Get standards-aware subnet facts from CIDR notation or a dotted-decimal mask. Inputs and results stay in your browser.
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Address range
- Input address
—- Network address
—- Broadcast address
—- First usable address
—- Last usable address
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Masking
- Canonical CIDR
—- Prefix length
—- Subnet mask
—- Wildcard mask
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Capacity
- Total addresses
—- Usable addresses
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Address classification
Input address
- Purpose
—- Effective registry block
—- RFC 1918 private
—- Globally reachable
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Calculated subnet
- Coverage
—- Effective classifications
—- Classification segments
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Registry fields, subnet segments, and source
- References
- —
- Source allowed
- —
- Destination allowed
- —
- Forwardable
- —
- Globally reachable
- —
- Reserved by protocol
- —
- Registry status
- —
- Historical class
- —
Subnet classification map
Snapshot: —. Effective input record source: —.
Binary detail
- Input
—- Mask
—- Network
—- Range end
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Calculation contract
Clear behavior at every prefix.
The calculator accepts a host address inside a subnet and derives its canonical network. It never silently changes the address you entered.
Point-to-point links
Both addresses are usable endpoints under RFC 3021. No address is presented as a broadcast.
Host routes
The single address is the complete route. It has no separate network or broadcast reservation.
Operational reference
What the calculator accepts and returns.
Use the result as a compact subnet record: the entered address stays visible, the canonical network is separate, and unusual behavior includes its governing assumption.
Enter either supported format
Use combined CIDR notation such as 192.168.1.10/24, or enter an IPv4 address with a dotted-decimal mask such as 255.255.255.0.
Masks must be contiguous. Multi-digit octets and prefixes with leading zeros are rejected rather than interpreted ambiguously.
Inspect the complete subnet
Results include the canonical CIDR, network and range end, broadcast behavior, first and last usable addresses, subnet and wildcard masks, capacity, and binary values.
Every individual value and the complete engineering summary can be copied.
Keep classification in context
The input address uses the most-specific reviewed IANA designation. The full calculated subnet is analyzed separately and labeled uniform or mixed.
RFC 1918 membership and IANA Globally Reachable are separate facts. Neither one proves whether a route is currently reachable.
Worked example
192.168.1.10/24
The entered host address belongs to the canonical network 192.168.1.0/24. Under traditional subnet semantics, the first and final addresses are reserved as the network and broadcast addresses.
- Subnet mask
255.255.255.0- Wildcard mask
0.0.0.255- Broadcast
192.168.1.255- Usable range
192.168.1.1–192.168.1.254- Total addresses
256- Usable addresses
254
Evidence
Standards and registry sources
Subnet arithmetic is deterministic and browser-local. Address-purpose labels come from reviewed local snapshots, so a calculation never contacts IANA.
Common questions
IPv4 subnet calculator behavior
Can I enter a host address instead of a network address?
Yes. The calculator preserves the address you entered and derives the canonical network that contains it. VLSM planning uses a stricter contract and requires a canonical parent network.
Why does a /31 show two usable addresses?
RFC 3021 defines both addresses on a point-to-point `/31` as endpoints. The calculator therefore shows Endpoint A and Endpoint B and does not label either one as a broadcast.
How is a /32 handled?
A `/32` identifies one host-route address. It has one total and usable address, with no separate network or broadcast reservation.
Does “not RFC 1918” mean the address is public?
No. An address may instead be loopback, link-local, shared, documentation, benchmarking, multicast, reserved, or another special-purpose designation. The calculator reports those facts without claiming live Internet routability.