@james A tablespoon is half an ounce. An ounce is 30g (28.4 but CEFGW). So a Tbsp is 15g. Q.E.D.

I do a lot of baking using American recipes and this is the correct conversion factor.

@james …I realized I should show a little more of my work. Ounces is both a weight and volume measure. They are equal for water or anything with the same density of water. The density of butter - indeed the density of anything you're likely to bake with - differs by no more than a few percent.

So if a recipe calls for, say, 1/4 cup of butter, it's perfectly fine to treat that as 2oz (weight) ≈ 60g.