How do you write 12345678 in short word form?

Answer 1

You say either 'one,two,three,four,five,six,seven .& eight'. or

Twelve million, three hundred and forty five thousand, six hundred and seventy eight.

The top just gives a string of numbers, however, the bottom gives the numbers their correct unit names.

Answer 2

12 million, 345 thousand, 678.