How do you pronounce the number 9719278965.651007643?

Answer 1

The spelling can be too complex using decimal names, but would be (in the US)

"nine billion, seven hundred nineteen million, two hundred seventy-eight thousand, nine hundred sixty-five and six hundred fifty-one million, seven thousand, six hundred forty-three billionths."

If it was being spoken (transcribed), normally it would be stated by digits:

"nine, seven one nine, two seven eight, nine six five, point six five one, zero zero seven, six four three." (using a 3-digit grouping, which can also be 4 or 5 at a time).