Skip to content
ENExplore Calculators

IP Address Plan For Sites Calculator

Work out ip address plan for sites instantly with clear inputs, formula shown and shareable results.

About IP Address Plan For Sites Calculator

A multi-site plan reserves host bits for the largest site and site bits for the number of locations. Rounding both up to powers of two keeps every site summarisable behind one prefix, which is what makes WAN routing tables small. Utilisation above 100 percent means the parent block cannot hold the plan and you need a shorter base prefix.

Formula

Site plan

host bits = ceil(log2(hosts + 2)); site bits = ceil(log2(sites)); required prefix = 32 - (host bits + site bits)

Worked example

With the default values below, IP Address Plan For Sites Calculator returns Prefix per site of 24. Change any input above and every figure here is recalculated in your browser.

Inputs used

Number of sitesminimum 1
8
Hosts per siteminimum 1
200
Available block prefix (/n)accepts 8–28 bits
16 bits

Results

Prefix per site
24 /n
Addresses per site
256
Shortest prefix that holds the whole plan
21 /n
Utilisation of the available block
3.13%

Step by step

  1. 1Values used
  2. 2Site plan
  3. 3Prefix per site= 24 /n
  4. 4Addresses per site= 256
  5. 5Shortest prefix that holds the whole plan= 21 /n
  6. 6Utilisation of the available block= 3.13

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why round the site count up to a power of two?

Contiguous power-of-two allocation is what allows a single summary route per region. Nine sites need four site bits, giving room for sixteen and future growth.

Should every site get the same prefix?

A uniform prefix is simpler to operate and document. Use VLSM only where a handful of sites are dramatically larger than the rest.

Related Calculators

IP Address Plan For Sites Calculator | Calcrivo