How many usable hosts are in a /24 subnet?

A /24 has 256 addresses. Two are reserved for the network and broadcast addresses, leaving 254 usable hosts on a traditional network. On AWS, five addresses are reserved in every subnet, so a /24 gives 251 usable addresses.

What is CIDR notation?

CIDR (Classless Inter-Domain Routing) writes a network as an address followed by a slash and the number of fixed prefix bits, such as 10.0.0.0/16. The remaining bits identify hosts, so a smaller prefix number means a larger network.

What is a wildcard mask?

A wildcard mask is the inverse of the subnet mask. Where the subnet mask has 255, the wildcard has 0. Cisco ACLs and OSPF configurations use wildcard masks, for example 0.0.0.255 for a /24.

Which IP ranges are private?

RFC 1918 reserves 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 for private networks. These addresses are not routed on the public internet and are what you should use for cloud VPCs and home or office LANs.

Why do /31 and /32 have no broadcast address?

A /32 identifies a single host. A /31 is used for point-to-point links (RFC 3021) where both addresses are usable and no broadcast is needed, which saves addresses on router links.

IPv4 Subnet (CIDR) Calculator

Calculate network address, broadcast, usable host range, subnet mask and wildcard mask for any IPv4 CIDR block. Ideal for AWS, Azure and GCP VPC planning.

Built and maintained by TechVeb · Reviewed by Norina Aslam

IPv4 address with CIDR prefix

Network address	10.0.0.0/24
Subnet mask	255.255.255.0
Wildcard mask	0.0.0.255
Broadcast address	10.0.0.255
First usable host	10.0.0.1
Last usable host	10.0.0.254
Total addresses	256
Usable hosts	254
Usable on AWS (5 reserved)	251
Address type	Private (RFC 1918)
Binary mask	11111111.11111111.11111111.00000000

How to use the subnet calculator

Enter an IPv4 address followed by a prefix length, for example 192.168.1.10/24. The calculator shows the network and broadcast addresses, the first and last usable host, the subnet and wildcard masks, and how many hosts fit in the block. If you type a host address, it also tells you which network that host belongs to.

Planning subnets for AWS, Azure and Google Cloud

Give the VPC a large private block such as 10.0.0.0/16 so you can add subnets later.
Create separate public and private subnets in each availability zone, typically /20 to /24.
AWS reserves 5 addresses per subnet and Azure reserves 5; Google Cloud reserves 4. Plan for that overhead.
Never overlap CIDR blocks between VPCs you might later peer or connect over VPN.

Quick CIDR reference

Prefix	Subnet mask	Addresses
/16	255.255.0.0	65,536
/20	255.255.240.0	4,096
/24	255.255.255.0	256
/26	255.255.255.192	64
/28	255.255.255.240	16
/30	255.255.255.252	4

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