How many teaspoons in one dash of garlic powder?

There's no standard conversion for "dash" to teaspoons. A dash is a very subjective measurement, typically meaning a very small amount, about the size of a pinch.

It's best to think of a dash as approximately 1/16 of a teaspoon.

However, if you're following a recipe that calls for a dash, it's always better to err on the side of caution and start with a smaller amount. You can always add more later if needed.