How do you write 13.7 in word form?

Answer 1

"One hundred and thirty-seven". Or "one hundred, thirty-seven". (if the number modifies a larger number, use the "and", as in "one hundred and thirty-seven thousand"). For room numbers, employee ID numbers, and so forth, a simple "one three seven" or "one thirty seven" can be used.

Answer 2

Thirteen and seven tenths OR

Thirteen and seven OR

Thirteen point seven OR

Thirteen decimal seven

Different people will say it different ways.