Why are phone and calculator keypads upside down from each other?

The layout with 7-8-9 on top came from mechanical calculators and cash registers, which existed before push-button phones. Clerks who entered numbers quickly were already used to it, and electronic calculators kept the same arrangement. The number keys on the right side of a computer keyboard use it too.

ITU-T E.161, the international standard for phone keypads, acknowledges this. For devices used mainly for entering data, it allows the calculator-style layout, with the first and third rows swapped, as an exception.

In the late 1950s, as Bell Laboratories in the US developed push-button phones to replace the rotary dial, it built 16 different layouts, including rows, circles, triangles, and even one shaped like a dial, and had people try them. In a study published in 1960, the differences in speed between layouts were very small, but the one with 1-2-3 on top was slightly faster and more popular. Starting at the top left, the way we read, felt natural.

Push-button phone service first launched in Pennsylvania in November 1963, and that layout has carried on to smartphone dial screens, door locks, and ATM keypads.

Many people think phones deliberately flipped the calculator layout. But Bell Laboratories based its choice not on clerks who were used to calculators, but on ordinary people pressing number buttons for the first time. The result simply differed from the cash register tradition. There was no intent to make it the opposite.

Even though the two layouts are flipped top to bottom, the 5 sits in the same spot in the middle. The ITU standard recommends a small raised dot on the 5 key so that blind and visually impaired people, or anyone dialing in low light, can find the buttons. If you run a fingertip over a phone or a keyboard's number keys, you can often feel a bump on the 5.

Switching between the two layouts can sometimes send your finger to the wrong spot. Remembering that only the top and bottom rows swap around the 5 makes it less confusing.