CIDR Cheat Sheet for Common Subnet Sizes

This cheat sheet gives you the most commonly used CIDR ranges along with their subnet masks, block sizes, and usable host counts.

It is designed for quick reference when working with firewalls, cloud networking, VLANs, or troubleshooting IP ranges.

CIDR   Subnet Mask         Total IPs   Usable Hosts   Block Size

/30    255.255.255.252     4           2              4
/29    255.255.255.248     8           6              8
/28    255.255.255.240     16          14             16
/27    255.255.255.224     32          30             32
/26    255.255.255.192     64          62             64
/25    255.255.255.128     128         126            128
/24    255.255.255.0       256         254            256

CIDR   Subnet Mask         Total IPs   Usable Hosts

/23    255.255.254.0       512         510
/22    255.255.252.0       1024        1022
/21    255.255.248.0       2048        2046
/20    255.255.240.0       4096        4094
/16    255.255.0.0         65536       65534

Block sizes double as the subnet gets larger. Each step up halves the number of networks and doubles the number of hosts.

/30 → 4
/29 → 8
/28 → 16
/27 → 32
/26 → 64
/25 → 128
/24 → 256

• /24 is the most common subnet (256 addresses)
• /27 and /28 are common for smaller segments
• /30 is often used for point-to-point links
• For traditional IPv4 subnets larger than /31, subtract 2 addresses for network and broadcast
• /31 and /32 are special cases, so do not apply the usual host-count shortcut blindly

• /30 → point-to-point links
• /29 → very small networks
• /27 → small office segments
• /24 → standard LAN or VLAN
• /16 → large internal networks

Use the cheat sheet as a fast reference, but always confirm the actual network boundary for the specific IP you are working with. The same /27 size can begin at many different address boundaries depending on the source network.

It also helps to remember that usable host counts normally exclude the network and broadcast addresses in traditional IPv4 subnetting. That distinction matters when sizing VLANs, firewall objects, and cloud network segments.

If you are working with /31 or /32, handle them deliberately. Those prefixes are valid but behave differently from the everyday subnet sizes most cheat sheets are written for.

Instead of memorising everything, you can instantly calculate subnet ranges with the DNS Pro Subnet Calculator.

Enter an IP address with CIDR or subnet mask to get the full range, broadcast address, and usable hosts.

• What Is CIDR Notation?
• What Is a Subnet Mask?
• How to Calculate a Subnet Range

If you want to validate this topic in practice, these DNS Pro tools are the fastest next step.

• Subnet Calculator
• CIDR Converter
• Private vs Public IP Checker