How many hosts can a /24 subnet have?

A /24 subnet contains 256 total IP addresses (2^8 = 256). Two addresses are reserved: the network address (e.g. 192.168.1.0) and the broadcast address (e.g. 192.168.1.255). This leaves 254 usable host addresses. A /24 is the most common subnet size for home and small office networks.

How do I plan subnets for an AWS VPC?

For an AWS VPC, start with a /16 CIDR block (e.g. 10.0.0.0/16) and split it into tiers: public subnets for load balancers and NAT gateways, private subnets for application servers and ECS tasks, and isolated database subnets for RDS, ElastiCache, and OpenSearch. For high availability, replicate each tier across at least two Availability Zones. Use the AWS VPC Subnet Planner on this page to generate ready-to-use subnet CIDRs for 2, 4, 6, or 8 subnets.

OpsBash.com ⚡ Free Tools

Buy me a Koffee

Free CIDR & Subnet Calculator

CIDR & Subnet Calculator

Q: How do I calculate a subnet mask from CIDR prefix?

To convert a CIDR prefix length to a subnet mask, set that many leading bits to 1 in a 32-bit number. For /24: 11111111.11111111.11111111.00000000 = 255.255.255.0. For /16: 255.255.0.0. For /8: 255.0.0.0. The number of host addresses equals 2 raised to the power of (32 minus the prefix), minus 2 for the network and broadcast addresses.

Q: What is the difference between IPv4 and IPv6 subnetting?

IPv4 uses 32-bit addresses (e.g. 192.168.1.0/24) with prefix lengths from /0 to /32, and reserves both a network address and a broadcast address, reducing usable hosts by 2. IPv6 uses 128-bit addresses (e.g. 2001:db8::/32) with prefix lengths from /0 to /128. IPv6 has no broadcast address. The entire range is usable. IPv6 subnets are typically /64, giving each one 2^64 addresses.

Calculate subnet details, usable hosts, and split CIDRs instantly. Supports both IPv4 and IPv6. No sign-up required, runs entirely in your browser.

IP / CIDR Notation

Total Hosts

—

Usable Hosts

—

Network Class

—

Subnet Details

Binary Representation

Visual Subnet Splitter

Split a CIDR block into 2, 4, or 8 equal subnets. Works for IPv4 and IPv6.

AWS VPC Subnet Planner

Optimal subnet splits for public, private, and database tiers across Availability Zones.

Common Examples

Click any example to load it into the calculator above.

Usable Hosts

What is CIDR Notation?

CIDR (Classless Inter-Domain Routing) notation represents an IP address and its network prefix length in the format IP/prefix, for example 192.168.1.0/24. The prefix number indicates how many bits are used for the network portion, with the remaining bits available for host addresses.

How to Calculate Subnet Size from CIDR

The number of total addresses in a subnet equals 2 raised to the power of the host bits (32 minus the prefix for IPv4). For example, a /24 subnet has 2^8 = 256 total addresses and 254 usable hosts after subtracting the network and broadcast addresses.

CIDR Prefix	Total Addresses	Usable Hosts	Common Use
/8	16,777,216	16,777,214	Large private network (Class A)
/12	1,048,576	1,048,574	Medium private network (Class B)
/16	65,536	65,534	AWS VPC typical size
/20	4,096	4,094	AWS subnet typical size
/24	256	254	Home and small office network
/28	16	14	Small AWS subnet
/30	4	2	Point-to-point links
/32	1	0	Single host route

RFC 1918 Private IP Address Ranges

RFC 1918 defines three private IP address ranges that are not routable on the public internet. These ranges are used for internal networks, cloud VPCs, and home networks.

Range	Subnet Mask	Total Hosts	Common Use
10.0.0.0/8	255.0.0.0	16,777,214	Large enterprise networks
172.16.0.0/12	255.240.0.0	1,048,574	Medium networks
192.168.0.0/16	255.255.0.0	65,534	Home and small office

Click any range to load it into the calculator above.

AWS VPC Subnetting Guide

AWS reserves 5 IP addresses in every subnet: the network address, VPC router address, DNS server address, future use address, and broadcast address. A /24 subnet in AWS has 251 usable hosts instead of the standard 254.

VPC Size	Recommended Subnet Layout
/16 VPC	4x /18 subnets (16,382 hosts each)
/16 VPC	8x /19 subnets (8,190 hosts each)
/20 VPC	4x /22 subnets (1,022 hosts each)
/24 VPC	4x /26 subnets (59 hosts each)

What is VLSM (Variable Length Subnet Masking)?

VLSM allows network engineers to divide an IP address space into subnets of different sizes based on actual host requirements. This eliminates IP address waste compared to using a single fixed subnet size for all network segments.

Frequently Asked Questions

CIDR (Classless Inter-Domain Routing) notation is a compact way to express an IP address range. It consists of an IP address followed by a slash and a prefix length, for example 192.168.1.0/24. The prefix length indicates how many leading bits are the network portion. /24 means the first 24 bits identify the network, leaving 8 bits for host addresses (256 total IPs). CIDR replaced the older Class A/B/C system and allows more efficient allocation of address space.

Set the first N bits to 1, where N is the prefix length, in a 32-bit number. For /24: 11111111.11111111.11111111.00000000 = 255.255.255.0. For /16: 255.255.0.0. For /8: 255.0.0.0. The wildcard mask is the bitwise inverse — for /24 that's 0.0.0.255, useful in ACLs and firewall rules. This calculator shows both subnet and wildcard masks instantly.

IPv4 uses 32-bit addresses (e.g. 192.168.1.0/24) with prefix lengths from /0 to /32. It reserves one address for the network ID and one for broadcast, reducing usable hosts by 2. IPv6 uses 128-bit addresses (e.g. 2001:db8::/32) with prefix lengths from /0 to /128. IPv6 has no broadcast address. Every address in the range is usable. IPv6 subnets are typically /64, giving each network 2⁶⁴ ≈ 18 quintillion addresses. ISPs typically assign /48 or /56 prefixes to customers.

A /24 subnet contains 256 total IPs (2⁸ = 256). Two are reserved: the network address (e.g. 192.168.1.0) and the broadcast address (e.g. 192.168.1.255), leaving 254 usable host addresses. Common subnet sizes: /30 = 2 usable, /29 = 6, /28 = 14, /27 = 30, /26 = 62, /25 = 126, /24 = 254, /23 = 510, /22 = 1022, /21 = 2046, /20 = 4094, /16 = 65,534.

Start with a /16 VPC CIDR (e.g. 10.0.0.0/16) and create three tiers: Public subnets for ALBs and NAT gateways, Private subnets for application servers and ECS tasks, and Database subnets for RDS and ElastiCache. Replicate each tier across at least 2 Availability Zones for HA. A /16 split into /18s gives 4 subnets of 16,382 usable hosts each. Use the AWS VPC Subnet Planner above to generate CIDRs automatically.