Host Count Calculator
Find the total and usable host addresses available for any CIDR prefix length.
Inputs
Usable Hosts
254
Total Addresses
256
Subnet Mask
255.255.255.0
Note
Network and broadcast addresses excluded.
Step by step
Values used
CIDR Prefix = 24 /
Total and usable hosts
total = 2^(32 − prefix); usable = total − 2
Usable Hosts
= 254
Total Addresses
= 256
Subnet Mask
= 255.255.255.0
Note
= Network and broadcast addresses excluded.
How it works
Every IPv4 subnet of prefix length p contains 2^(32−p) total addresses. Of these, the first is the network address and the last is the broadcast address, neither of which can be assigned to a host — so usable hosts = 2^(32−p) − 2. The exceptions are /31 (RFC 3021 point-to-point links, both addresses usable) and /32 (a single host route).
Formula
Total and usable hosts
total = 2^(32 − prefix); usable = total − 2
- p
- CIDR prefix length
Frequently Asked Questions
Why subtract 2 from the total address count?
One address in every subnet is reserved as the network identifier and one as the broadcast address for that subnet, so they cannot be assigned to hosts.
How many usable hosts does a /24 have?
A /24 has 2^(32−24) = 256 total addresses, minus 2 reserved addresses, giving 254 usable hosts.
What's special about /31 and /32?
A /32 has only one address and identifies a single host (a 'host route'). A /31, per RFC 3021, is defined so both of its two addresses can be used as endpoints of a point-to-point link, since there's no room for separate network/broadcast addresses.