How do you spell 10 to 20?

You can't spell "10 to 20" in the traditional sense, as it's a range of numbers, not a single word.

However, you could describe it in these ways:

* "Ten to twenty" (this is how you would say it)

* "The teens" (this refers to the numbers 13 to 19)

* "From ten to twenty"

* "The range of numbers from ten to twenty"

It depends on the context and how you want to use it.