Hosts per subnet calculator
The Hosts per subnet calculator computes hosts per subnet from the relation 2^(32-p) - 2. It takes a single input (prefix length) and returns the usable hosts. These calculators are for network and systems administrators, software and hardware engineers, and computing students, turning a stated value, address, string or configuration into the exact figure, code or encoding that the rule behind it produces, without working it through by hand. Enter your values below and the result updates instantly, and you can share a permalink that pre-fills the exact calculation. Check the base, unit and width of each input before entering it: hexadecimal against decimal, bits against bytes, binary against decimal prefixes, and 0-based against 1-based positions are the usual sources of a wrong answer here, and a result that is out by a neat factor is far more often one of those than an arithmetic slip. For example, with prefix length = 8, the usable hosts works out to 16777214, and the worked example further down the page shows every step so you can follow the arithmetic and reproduce it by hand. This is a standard formula rather than a jurisdiction-specific rule, so it does not depend on an external rate or schedule, and the figure above each result carries the date it was last verified. The result follows the definition and the exact values you supply, so it can differ from what a live system reports: reserved and unusable values, protocol and filesystem overhead, the width and precision of the data type actually in use, and the conventions a particular language, device or display applies all sit outside the calculation, so confirm the figure against the environment it will be used in.
With Prefix length = 8, the result is 16777214.
Applies to: any numeric inputs. Method: a standard formula, not a jurisdiction-specific rule. How we document and test our methods, checked 2026-07-09.
The formula
2^(32-p) - 2
Worked example
With Prefix length = 8:
- 2^(32-p) - 2
- Usable hosts = 16777214
This worked example is one of the automated golden-value tests this calculator must pass before it can publish.
What this assumes
- Inputs are real numbers in the units shown.
- The result is the exact value of 2^(32-p) - 2; general information, not professional advice.
Frequently asked questions
What formula does this use?
2^(32-p) - 2. This is a standard formula rather than a jurisdiction-specific rule.
Does the result ever change over time?
No. This is a pure formula with no external rate, so the same inputs always give the same result.
Official sources and verification
- Method: a standard formula rather than a jurisdiction-specific rule; how we document and test our methods, checked 2026-07-09.
Reviewed by the CalculatorHub team, edited by James Graham, 2026-07-09. See our methodology. General information, not professional advice.