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CIDR and Subnet Mask Cheat Sheet

Every IPv4 prefix from /8 to /32 with its subnet mask, wildcard mask, address count and usable hosts, plus private and special ranges and quick sums.

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CIDR notation writes a network as an address plus a prefix length: 192.168.1.0/24 means the first 24 bits identify the network and the remaining 8 bits identify hosts. The prefix length is the number of 1 bits in the Subnet mask. Convert between them with the Subnet Mask ⇄ CIDR Converter, and plan a whole network with the IPv4 Subnet Calculator.

Prefix lengths from /8 to /32

CIDR Subnet mask Wildcard Addresses Usable hosts
/8 255.0.0.0 0.255.255.255 16,777,216 16,777,214
/9 255.128.0.0 0.127.255.255 8,388,608 8,388,606
/10 255.192.0.0 0.63.255.255 4,194,304 4,194,302
/11 255.224.0.0 0.31.255.255 2,097,152 2,097,150
/12 255.240.0.0 0.15.255.255 1,048,576 1,048,574
/13 255.248.0.0 0.7.255.255 524,288 524,286
/14 255.252.0.0 0.3.255.255 262,144 262,142
/15 255.254.0.0 0.1.255.255 131,072 131,070
/16 255.255.0.0 0.0.255.255 65,536 65,534
/17 255.255.128.0 0.0.127.255 32,768 32,766
/18 255.255.192.0 0.0.63.255 16,384 16,382
/19 255.255.224.0 0.0.31.255 8,192 8,190
/20 255.255.240.0 0.0.15.255 4,096 4,094
/21 255.255.248.0 0.0.7.255 2,048 2,046
/22 255.255.252.0 0.0.3.255 1,024 1,022
/23 255.255.254.0 0.0.1.255 512 510
/24 255.255.255.0 0.0.0.255 256 254
/25 255.255.255.128 0.0.0.127 128 126
/26 255.255.255.192 0.0.0.63 64 62
/27 255.255.255.224 0.0.0.31 32 30
/28 255.255.255.240 0.0.0.15 16 14
/29 255.255.255.248 0.0.0.7 8 6
/30 255.255.255.252 0.0.0.3 4 2
/31 255.255.255.254 0.0.0.1 2 2
/32 255.255.255.255 0.0.0.0 1 1

Usable hosts are the addresses minus two: the first is the network address and the last is the broadcast address. A /31 has two usable addresses for point-to-point links (RFC 3021) and a /32 is a single host.

Quick sums

  • Addresses in a prefix: 2 to the power of (32 minus the prefix). A /26 has 26 = 64 addresses and 62 usable hosts.
  • Block size in the interesting octet is 256 minus the mask's value in that octet. For 255.255.255.192 it is 256 - 192 = 64, so /26 subnets start at 0, 64, 128 and 192.
  • Wildcard mask is the mask with every bit flipped (used in router access lists).
  • Splitting a network. Each extra prefix bit halves the block: a /24 becomes two /25, four /26 or eight /27.

Ranges with a special meaning

Range Meaning
10.0.0.0/8 Private (RFC 1918)
172.16.0.0/12 Private (RFC 1918)
192.168.0.0/16 Private (RFC 1918), home networks
100.64.0.0/10 Carrier-grade NAT (RFC 6598)
127.0.0.0/8 Loopback (this computer)
169.254.0.0/16 Link-local (no DHCP answer)
224.0.0.0/4 Multicast
192.0.2.0/24 Documentation (TEST-NET-1)
198.51.100.0/24 Documentation (TEST-NET-2)
203.0.113.0/24 Documentation (TEST-NET-3)

Addresses in the private ranges are not routed on the public internet, which is why home routers translate them with NAT. To check whether an address falls inside a block, use the IP in CIDR Checker; for the full method, see How Subnetting Works.

Try these tools

Subnet Mask ⇄ CIDR Converter

Convert between a dotted-decimal subnet mask (255.255.255.0) and CIDR prefix notation (/24) instantly.

IPv4 Subnet Calculator

Professional IPv4 subnet calculator for network administrators.

IP in CIDR Checker

Check whether IPv4 or IPv6 addresses fall inside CIDR ranges, for many addresses and ranges at once.

IP Range to CIDR Converter

Convert a first-last IP address range into the minimal set of covering CIDR blocks.

CIDR Aggregator

Merge a list of CIDR blocks into the minimal set of covering supernets.

IPv4 to Binary Converter

Convert a dotted-decimal IPv4 address to its 32-bit binary octet representation, or back again.

IP Address Sorter

Sort a list of IPv4 addresses numerically (not alphabetically), with optional deduplication and descending order.

IP Address to Hex Converter

Convert a dotted-decimal IPv4 address to hexadecimal notation, or decode a hex value back to an IP address.

See also

  • Glossary Subnet mask
    A subnet mask is a 32-bit value that marks which part of an IPv4 address identifies the network and which part identifies the host.
  • Glossary CIDR
    CIDR (Classless Inter-Domain Routing) is the notation that writes an IP network as an address plus a prefix length, such as 192.168.1.0/24.
  • Glossary NAT
    NAT (Network Address Translation) lets many devices with private IP addresses share one public IP address by rewriting addresses and ports.
  • Guide How Subnetting Works
    How an IP address splits into network and host parts, how to find a network and broadcast address.
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