According to Joe Smith, if it's more than one, you're doing it wrong.
Smith, a lawyer from Oregon, gave a lightning-quick TEDx talk in 2012 where he demonstrated his fool-proof method for using just one paper towel to dry your hands.
Around the world, humans use roughly 13 billion paper towels a year. If everyone managed to use one fewer paper towel per day, Smith says, we could cut our yearly paper towel consumption by 571 million pounds.
It's not that hard.
Step one: Shake your hands 12 times to get the excess water off.
Step two: Fold one paper towel in half. It allows for interstitial suspension, a fancy way of saying it absorbs better.
Step three: Use one side of the towel to dry one hand, and the flip side for the other.
Shake and fold, it's that simple.
"You will for the rest of your life remember those words every time you pick up a paper towel," Smith says, before hinting at the next practice he plans to conquer: "Toilet paper."