Have you ever wondered why does a calculator and a touch-tone telephone have exactly opposite layout for their keypads? While the calculator keypad starts from 1-2-3 at the lower row, the telephone keypad starts from 1-2-3 at the top row.

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There are many theories which try to reason the difference between the layouts, or was it just intentional and an honest mistake?

The most viable theory dates back to the time when engineers used mechanical calculators which had multiple columns of keys (usually 8 columns), with each column having 9 keys corresponding to the 9 digits i.e 1 to 9. They generally had to deal with large numbers which had a lot of trailing zeroes.

There was no key to represent zero as it was implicit that if a user didn’t press any key then it meant the digit represented by that column was zero.

The highest number 9 was placed on the top and 1 being of the lowest value, was placed at the bottom.


With time and advent of technology, engineers were able to replace mechanical parts with , electronic circuit, electronic displays and did way with the redundant keys. The new electronic calculator had just 10 keys for 10 numbers which were displayed on the sophisticated LED light.

Since the mechanical calculators had 0 at the bottom and 9 on top, the engineers of electronic calculator followed the same norm  so that engineers & scientists migrating to these new calculators would not face any substantial issue.


So, why did the engineers didn’t follow the same layout while producing a telephone? As you know, early telephones had rotary dial, which was basically mechanical design with moving parts.


With time and technology, phone companies replaced the rotary dial with numerical keypad but were not able to narrow down on it’s layout. While some suggested a 5×2 matrix (5 rows, 2 columns), some thought 3×3 matrix would be fine, while few others thought just replicating the calculator layout would be good enough.

The engineers the experimented with several layouts and invited people to use them & provide their feedback.


The experiment made it clear that people were more comfortable with a keypad layout which had 1-2-3 on top. The Bell engineers then adopted the 1-2-3 on top layout which is still in use today and has been adapted to cellphones as well.