A postcard-sized idea met a network-sized constraint
The postcard comparison offered a practical way to think about a short message: people could often fit a brief note on a postcard using a typewriter. But the familiar 160-character limit also reflected how mobile networks were built to carry SMS. Text messages were designed to use a small amount of data, sent through the network’s signaling system—the channel phones use to coordinate calls and other operations—rather than requiring a full voice connection.
Why the number was 160
An SMS message could carry 140 bytes of data. For ordinary English letters and common symbols, the system used a compact encoding that represented each character in seven bits. That allowed 160 characters to fit into the available space. Characters outside that compact set, such as many accented letters and non-Latin scripts, could require a different encoding and reduce the number that fit.
Longer messages had to be stitched together
When a message exceeded the limit, phones and networks could split it into several SMS messages and reassemble them on the recipient’s phone. Each segment needed information identifying it as part of a larger message, so a joined message typically held fewer than 160 characters per segment—often 153 in the common seven-bit encoding.
That is why a text that looked like one continuous note could count as multiple messages: the postcard-sized idea shaped the limit, while the network’s small data packets determined how it worked in practice.
