A dotted quad is a way of writing an IPv4 internet address as four numbers separated by periods, like 192.168.1.1. Each number ranges from 0 to 255, and there are always exactly four of them, which is where the “quad” comes from. You see this format every time you configure a Wi-Fi network, set up a router, or check your computer’s IP address.
How Dotted Quad Notation Works
Every device connected to the internet using IPv4 gets a unique address that is, at its core, a 32-digit binary number: a long string of ones and zeros. That raw format is nearly impossible for humans to read or type without making mistakes. Dotted quad notation solves this by splitting those 32 binary digits into four groups of eight (called octets), then converting each group into a regular decimal number.
Eight binary digits can represent values from 0 (00000000) to 255 (11111111), so each of the four numbers in a dotted quad falls within that range. The four numbers are separated by periods. For example, the binary address 11000001010000010100100000011011 becomes 193.65.72.27 in dotted quad form. Much easier to work with.
Why the Limit Is 255
The cap of 255 per segment isn’t arbitrary. Each octet is 8 bits long, and 8 bits can store 256 possible values (0 through 255). You’ll never see a valid IPv4 address with a number like 312 or 999 in any position. If you spot one, it’s a typo or a scam. The total number of unique IPv4 addresses this system allows is about 4.3 billion (256 × 256 × 256 × 256), which seemed like plenty in 1981 when the format was standardized in RFC 791 but has long since been exhausted.
Dotted Quad vs. Dotted Decimal
“Dotted quad” and “dotted decimal” mean the same thing. Both describe IPv4 addresses written as four decimal numbers separated by dots. “Dotted quad” emphasizes that there are four segments. “Dotted decimal” emphasizes that the numbers are in base-10 rather than binary or hexadecimal. You’ll see both terms in networking documentation, textbooks, and configuration guides, and they’re interchangeable.
What Each Part of the Address Means
An IPv4 address isn’t just a random ID. It contains two pieces of information baked into its structure: a network portion and a host portion. The network portion identifies which network the device belongs to (think of it like a zip code), while the host portion identifies the specific device on that network (like a street address).
Where the split happens between network and host depends on the subnet mask, which is itself written in dotted quad notation. A subnet mask of 255.255.255.0, for instance, means the first three octets identify the network and the last octet identifies individual devices. This is why network administrators work with dotted quads constantly: both IP addresses and subnet masks use the same format.
How Domain Names Replace Dotted Quads
In everyday browsing, you rarely type a dotted quad directly. Instead, you type a domain name like google.com, and the Domain Name System (DNS) translates that into the corresponding dotted quad address behind the scenes. This translation is why the Oxford Reference notes that dotted quad notation is “only rarely used” by end users: meaningful names are easier to remember than strings of numbers. But under the hood, every connection your device makes still relies on that four-number address.
Why IPv6 Uses a Different Format
IPv6 was created to replace IPv4 because 4.3 billion addresses weren’t enough for a world full of phones, laptops, smart devices, and sensors. IPv6 addresses are 128 bits long instead of 32, which means they’re four times as large and support a vastly larger address space. Writing a 128-bit address as dotted quad notation would produce 16 decimal numbers in a row, which would be unwieldy.
Instead, IPv6 uses a colon-hexadecimal format. The address is split into eight groups of four hexadecimal characters, separated by colons. A typical IPv6 address looks like 2001:0db8:85a3:0000:0000:8a2e:0370:7334. Hexadecimal (base-16) packs more information per character than decimal, keeping the addresses shorter than they’d otherwise be. So the dotted quad is specifically an IPv4 convention. If someone mentions a dotted quad, they’re always talking about IPv4.