How many hosts fit in a /24?

254 usable: 256 addresses minus the network and broadcast addresses.

I need exactly 62 hosts. Is a /26 enough?

Yes, a /26 gives exactly 62 usable addresses, but with zero headroom. If anything else joins the VLAN (a gateway, a second router), you need a /25.

Why not just use a /16 for everything?

One huge broadcast domain amplifies ARP, broadcast and multicast traffic, and a loop or broadcast storm takes down every host. Smaller subnets contain failures.

Hosts to Subnet Mask Calculator: Prefix for N Hosts

The rule

A subnet with h host bits has 2^h addresses, two of which are reserved for the network and broadcast. To fit N hosts you need the smallest h that satisfies:

2^h − 2 ≥ N → h = ⌈log₂(N + 2)⌉ → prefix = 32 − h

Special cases: one host is a /32 and two hosts fit a /31 (RFC 3021, point-to-point only).

Worked example: 50 hosts

N + 2 = 52. The next power of two is 64 = 2⁶, so h = 6 and the prefix is /26 (mask 255.255.255.192). A /26 gives 62 usable addresses, leaving 12 spare (19.4%). The next size up, /25, gives 126 hosts.

Reference table

Prefix	Mask	Addresses	Usable hosts
/30	255.255.255.252	4	2
/29	255.255.255.248	8	6
/28	255.255.255.240	16	14
/27	255.255.255.224	32	30
/26	255.255.255.192	64	62
/25	255.255.255.128	128	126
/24	255.255.255.0	256	254
/23	255.255.254.0	512	510
/22	255.255.252.0	1,024	1,022
/21	255.255.248.0	2,048	2,046
/20	255.255.240.0	4,096	4,094

Count more than end users

The host count a subnet must hold is rarely just the number of people. Before sizing, add:

The gateway address, plus two more if you run HSRP/VRRP (one per router plus the virtual IP).
Printers, APs, IP phones, cameras and IoT devices that share the VLAN.
DHCP churn: devices that reconnect with a new MAC (randomized MACs on phones and laptops) can hold leases until they expire.
Growth over the expected life of the design, typically three to five years.

A good rule of thumb is to size for 1.5× the current count, then round up to the next prefix. In RFC 1918 space, address scarcity is rarely the constraint; broadcast domain size is. Keeping user VLANs at /24 or smaller limits ARP and broadcast traffic and makes failure domains easier to reason about.

Exam shortcut

For CCNA-style questions, memorize the powers of two up to 2¹² (4,096). Add 2 to the host count, find the first power of two that is equal or larger, and subtract its exponent from 32. For 500 hosts: 502 → 512 = 2⁹ → /23. For 1,000 hosts: 1,002 → 1,024 = 2¹⁰ → /22. If the question also gives a number of subnets, check that the borrowed bits still leave enough room for both.

Applying it

! Cisco IOS DHCP pool for a /26
ip dhcp pool USERS
 network 10.10.20.0 255.255.255.192
 default-router 10.10.20.1

Hosts to subnet mask calculator