I have a recipe that calls for garlic powder, but I only have fresh garlic on hand.
What ratio should I use to substitute?
I'd say about 1 clove for every half-teaspoon of garlic powder. There isn't going to be anything particularly scientific about this, since garlic cloves vary in size, strength and flavor but that will be in the ballpark.
I'll typically get 1/3 the starting weight of the cloves ( weight before peeling ) once it's all dried and ground.
I've only weighed before and after twice though.
Method used: peel and slice garlic really thin (used a mandoline), spread out on a parchment lined baking sheet (heavy aluminum), bake at 170 F (lowest my oven would go). Remove when the dried garlic easily crumbles between your fingers (check every 15 min. after the first 45 min.). Then grind it up.
The other option I can think of...
Finely chop up some garlic and cook them in med-to-high temp oil. You may put in the garlic when the oil is warm, so you don't over cook. As soon as you see the colour of garlic turning to brown colour, remove it asap and get the garlic out of oil.
After that, you can use the same amount of the cooked garlic as the powder.
Another way is to roast your garlic and then chop it up which is closer to garlic powder