// FREE IT TOOLS

IP Subnet Calculator

Enter any IPv4 address in CIDR notation to instantly calculate the full subnet breakdown.

// ENTER NETWORK (CIDR NOTATION)

examples:

Enter a network in CIDR notation above to see results

Subnet Quick Reference

The table below lists the most commonly used CIDR prefixes, their subnet masks, usable host counts, and typical use cases in enterprise and SMB networks.

Common CIDR subnet prefixes — subnet mask, usable host count, and typical use case
CIDR	Subnet Mask	Usable Hosts	Typical Use
/8	255.0.0.0	16,777,214	Large corporate backbone
/16	255.255.0.0	65,534	Campus / data centre
/24	255.255.255.0	254	Small office LAN
/25	255.255.255.128	126	Split /24 — floor VLAN
/26	255.255.255.192	62	Department VLAN
/27	255.255.255.224	30	Printer or IoT pool
/28	255.255.255.240	14	Server cluster
/30	255.255.255.252	2	Point-to-point WAN link
/31	255.255.255.254	2	Point-to-point (RFC 3021)
/32	255.255.255.255	1	Single host / loopback

Understanding CIDR Notation

CIDR (Classless Inter-Domain Routing) notation expresses an IP address and its network prefix as a single string — for example, 192.168.1.0/24. The number after the slash is the prefix length: it defines how many bits identify the network, with the remaining bits available for hosts.

A /24 prefix means 24 bits are fixed (network) and 8 bits are variable (host), giving 2⁸ = 256 total addresses — 254 usable after reserving the network and broadcast addresses.

Private address ranges (RFC 1918) are reserved for internal use and are not routable on the public internet:

10.0.0.0/810.0.0.0 – 10.255.255.255 (16.7 million addresses)
172.16.0.0/12172.16.0.0 – 172.31.255.255 (1 million addresses)
192.168.0.0/16192.168.0.0 – 192.168.255.255 (65,536 addresses)

Special cases: /31 networks (RFC 3021) are used for point-to-point links where both addresses are usable host addresses. /32 denotes a single host and is commonly used in routing tables and firewall rules.

Frequently Asked Questions

What is a subnet mask?: A subnet mask is a 32-bit number that divides an IP address into a network portion and a host portion. Written in dotted-decimal notation (e.g. 255.255.255.0), it tells network devices which part of the address identifies the network and which part identifies the host. CIDR notation (e.g. /24) is shorthand for the same information.
What is the difference between a network address and a broadcast address?: The network address is the first address in a subnet — all host bits are zero. It identifies the subnet itself and cannot be assigned to a device. The broadcast address is the last address — all host bits are one. Messages sent to the broadcast address are delivered to every host on the subnet. Neither can be used for individual devices.
How many usable hosts does a /24 subnet have?: A /24 subnet contains 256 total addresses (2⁸). Two are reserved — the network address (x.x.x.0) and the broadcast address (x.x.x.255) — leaving 254 usable host addresses.
What is a wildcard mask?: A wildcard mask is the inverse of a subnet mask. Where the subnet mask uses 1s to mark the network bits, the wildcard mask uses 1s to mark the host bits. Wildcard masks are widely used in Cisco ACLs and OSPF area configuration. For a /24 subnet the wildcard mask is 0.0.0.255.
What does /30 mean in networking?: A /30 subnet contains 4 addresses: one network address, two usable host addresses, and one broadcast address. It is the smallest practical subnet for connecting two routers on a point-to-point WAN link, making efficient use of IP address space.

// CLOUD INFRASTRUCTURE

Designing or migrating a network?

DMC IT Services designs and manages cloud and on-premises network infrastructure for SMBs across London, Cambridge, Hertfordshire, and Bedfordshire — from initial IP addressing schemes through to Microsoft 365 and Azure deployments.

Talk to an Engineer

← Back to all free tools

Subnet Quick Reference

The table below lists the most commonly used CIDR prefixes, their subnet masks, usable host counts, and typical use cases in enterprise and SMB networks.

Common CIDR subnet prefixes — subnet mask, usable host count, and typical use case
CIDR	Subnet Mask	Usable Hosts	Typical Use
/8	255.0.0.0	16,777,214	Large corporate backbone
/16	255.255.0.0	65,534	Campus / data centre
/24	255.255.255.0	254	Small office LAN
/25	255.255.255.128	126	Split /24 — floor VLAN
/26	255.255.255.192	62	Department VLAN
/27	255.255.255.224	30	Printer or IoT pool
/28	255.255.255.240	14	Server cluster
/30	255.255.255.252	2	Point-to-point WAN link
/31	255.255.255.254	2	Point-to-point (RFC 3021)
/32	255.255.255.255	1	Single host / loopback

Understanding CIDR Notation

A /24 prefix means 24 bits are fixed (network) and 8 bits are variable (host), giving 2⁸ = 256 total addresses — 254 usable after reserving the network and broadcast addresses.

Private address ranges (RFC 1918) are reserved for internal use and are not routable on the public internet:

10.0.0.0/810.0.0.0 – 10.255.255.255 (16.7 million addresses)
172.16.0.0/12172.16.0.0 – 172.31.255.255 (1 million addresses)
192.168.0.0/16192.168.0.0 – 192.168.255.255 (65,536 addresses)

Frequently Asked Questions

What is a subnet mask?

A subnet mask is a 32-bit number that divides an IP address into a network portion and a host portion. Written in dotted-decimal notation (e.g. 255.255.255.0), it tells network devices which part of the address identifies the network and which part identifies the host. CIDR notation (e.g. /24) is shorthand for the same information.

What is the difference between a network address and a broadcast address?

The network address is the first address in a subnet — all host bits are zero. It identifies the subnet itself and cannot be assigned to a device. The broadcast address is the last address — all host bits are one. Messages sent to the broadcast address are delivered to every host on the subnet. Neither can be used for individual devices.

How many usable hosts does a /24 subnet have?

A /24 subnet contains 256 total addresses (2⁸). Two are reserved — the network address (x.x.x.0) and the broadcast address (x.x.x.255) — leaving 254 usable host addresses.

What is a wildcard mask?

A wildcard mask is the inverse of a subnet mask. Where the subnet mask uses 1s to mark the network bits, the wildcard mask uses 1s to mark the host bits. Wildcard masks are widely used in Cisco ACLs and OSPF area configuration. For a /24 subnet the wildcard mask is 0.0.0.255.

What does /30 mean in networking?

A /30 subnet contains 4 addresses: one network address, two usable host addresses, and one broadcast address. It is the smallest practical subnet for connecting two routers on a point-to-point WAN link, making efficient use of IP address space.