IP & Domain Tools

CIDR Prefix to Hosts Calculator

Pick a prefix length and see the address count, usable hosts and mask.

By TheCalcTools Updated Formula checked and tested

Your numbers

Your results

Total addresses
Total addresses
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Usable hosts
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Subnet mask
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Equivalent /24 networks
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CIDR Prefix to Hosts Calculator by TheCalcTools

How the CIDR Prefix to Hosts Calculator works

Enter the prefix length shown after the slash in CIDR notation.

The number of host bits is 32 minus the prefix.

Each extra host bit doubles the block size.

The formula

Total addresses = 2^(32 − n)Usable hosts = 2^(32 − n) − 2

Worked example

Using the default values shown in the calculator:

Prefix length (/n)22
  1. A /22 leaves 32 − 22 = 10 host bits.
  2. 2^10 = 1,024 addresses, so 1,022 usable hosts.
  3. The mask is 255.255.252.0, equal to 4 /24 networks.

Result:

Total addresses1,024
Usable hosts1,022
Subnet mask255.255.252.0
Equivalent /24 networks4.0000

Frequently asked questions

How many addresses are in a /24?

256 addresses, 254 of them usable for hosts.

What prefix do I need for 500 hosts?

You need at least 502 addresses, so 2^9 = 512 fits: a /23.

Sources and further reading

IPv4 Subnet CalculatorEnter an IPv4 address and prefix length to get the network, broadcast, mask and host… Subnet Mask to CIDR Prefix CalculatorEnter a subnet mask to get the CIDR prefix, wildcard mask and usable hosts Hosts to Subnet Prefix (VLSM) CalculatorEnter hosts needed and growth to get the right subnet size Subnet Split Calculator (Equal Subnets)Divide a parent network into the number of equal subnets you need

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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.