Network Size Calculator

• IPv4 total addresses: Total = 2^{(32 − prefix)}.
• IPv4 usable hosts (standard): Usable = Total − 2 (network and broadcast), for prefixes ≤ /30.
• IPv4 /31 note: Two-address point-to-point links can treat both as usable.
• IPv6 total addresses: Total = 2^{(128 − prefix)} (reported as a power of two).
• Design from requirements: Choose smallest power-of-two Total ≥ (required + reserved + overhead).
• Optional supernet sizing: Supernet Total ≥ (subnets × addresses-per-subnet).

1. Select Analyze subnet to evaluate an existing prefix.
2. Pick IPv4 or IPv6, then enter the prefix length.
3. Optionally provide a base address to compute IPv4 range values.
4. Select Design from requirements to size a subnet from capacity needs.
5. Enter required hosts, reserved space, and subnets; then submit.
6. Use the CSV or PDF buttons to export your latest results.

Capacity starts with bits

Network size is driven by address bits and prefix length. For IPv4, a /24 leaves 8 host bits, producing 2^(32−24)=256 addresses. For IPv6, a /64 leaves 64 bits, yielding 2^64 addresses, which is about 1.84×10^19. This calculator converts those relationships into totals, usable counts, and planning-friendly summaries.

IPv4 practical sizing

In many routed IPv4 segments, two addresses are reserved for the network and broadcast. That makes a /24 provide 254 usable hosts, while a /28 provides 14. If you enter a base address, the tool derives the network boundary and shows first and last usable values. For point-to-point links, /31 can make both addresses usable, avoiding wasted space.

IPv6 planning perspective

IPv6 does not run out of hosts in the same way, so engineers often standardize subnet boundaries for simplicity. A common practice is allocating /64 per LAN, then grouping sites under a larger block such as /56 or /48. Instead of listing every address, the calculator reports powers of two, approximate magnitude, and digit count so teams can compare prefix choices without losing scale.

Designing with reserves

Right-sizing begins with demand, then adds safety margin. If a VLAN needs 50 devices and you reserve 10 for infrastructure and growth, the requirement becomes 60 usable. The calculator selects the smallest power-of-two subnet meeting that target, then reports total and usable capacity. This mirrors procurement-style capacity planning where headroom reduces readdressing during expansion.

Subnet count and supernets

Multiple subnets should roll up cleanly for routing. If you need 4 equal /26 subnets, the aggregate is 4×64=256 addresses, which aligns with a /24 supernet. The tool estimates an optional supernet prefix so you can summarize routes, document allocations, and keep tables consistent across environments. This supports growth planning when additional subnets are expected later.

Operational checks and exports

After sizing, validate implementation details: DHCP scope excludes reserved ranges, gateways and critical services are fixed, and security policies match the boundary. Use the results panel to capture the chosen prefix, mask, and computed ranges. The chart visualizes capacity tradeoffs at a glance, while CSV and PDF exports provide auditable documentation for change reviews and handoffs for your team.

What is the difference between total and usable IPv4 addresses?

Total addresses come from 2^(32−prefix). Usable hosts usually exclude the network and broadcast addresses, so usable equals total minus two for prefixes up to /30.

Why does /31 show two usable addresses?

On point-to-point links, RFC-style behavior allows both addresses to be assigned because no broadcast is needed. That can save space compared with /30.

Should I always use /64 for IPv6 subnets?

Many LAN designs standardize on /64 for compatibility and simplicity, but other prefixes can be valid for special cases. Follow your platform guidance and routing plan.

How do reserved addresses affect sizing?

Reserved space is added to required hosts before choosing the smallest fitting subnet. This headroom supports gateways, services, and growth without frequent readdressing.

What does the suggested supernet mean?

It is an optional aggregate block that can contain all planned equal-sized subnets. Using it can simplify route summaries and documentation, especially across multiple sites.

Can I export results for documentation?

Yes. After a calculation, use the CSV or PDF buttons in the results panel to save the latest output for change tickets, audits, or handoffs.