how much powdered gelatin to one gelatin leaf?

Some recipes call for a number of gelatin leaves, but since I use powdered gelatin I'd like to know the conversion rate/scaling.

According to Modernist Pantry and thanks to SAJ14SAJ:

for most of us the first gelatin we used was store bought granulated gelatin. This gelatin is 225 bloom and can be converted to sheet gelatin pretty easily.

1 (0.25 oz. ≈ 7.1 g) envelope granulated gelatin
= 1 tablespoon [(15 ml)] powdered gelatin
= 3 sheets leaf gelatin.

and so one sheet of leaf gelatin would correspond to ~1 teaspoon (5 ml) or 2.36g of powdered gelatin, taking Knox as the reference for granulated gelatin, with a Bloom strength of 225, which is closest to platinum-strength gelatin sheets.

And a bit extra info from Modernist Cuisine

Gelatins are measured by what is called their Bloom strength (usually labeled as bronze, silver, gold, or platinum). Knox brand has a bloom strength of 225. If you are making a recipe (not just one of ours, but any recipe), be it a Jell-O wreath or a pâté, you can use a different Bloom strength than what the recipe calls for, but you’ll have to do a little math. You can convert the recipe to use whatever gelatin you have on hand if you know the weight (MA) and Bloom strength (BA).

For gelatin A, you can find the equivalent weight of gelatin B (MB) with a Bloom strength of BB by using the formula MB = MA × BA ÷ BB. For example, if a recipe calls for 2.6 g of Knox gelatin, you could use 3.7 g of silver gelatin, which has a Bloom strength of 160 (2.6 × 225 ÷ 160 = 3.7). To make a vegetarian panna cotta, we substitute 0.8 g agar and 0.65 g xanthan for the 4.3 g gelatin the recipe normally calls for.

Example of sheet-to-powder calculations

Knowing that often 1 platinum sheet (again, roughly Knox equivalent) is 1.75g, I recently used the following calculations to figure out what the non-standard 6g of gelatin sheets in a recipe was equivalent to.

grams per platinum gelatin sheet sheets
1.75g 1 sheet
6g ?

6g of gelatin sheets * 1 sheet / 1.75g ≈ 3.43 sheets

Then, based on the Modernist Pantry numbers at the start of this answer:

grams of granulated gelatin sheets
7.1g 3 sheets
? 3.43 sheets

3.43 sheets * 7.1 g / 3 sheets = 8.1 g of Knox granulated gelatin.