hey, the number of grams depends on the type of sugar you're using. they all have different densities, so a tablespoon of each will have a different weight.
for standard granulated white sugar, a tablespoon is about 12.5 grams. if the recipe calls for packed brown sugar, it's a bit heavier at around 14 grams per tablespoon. powdered sugar is much lighter, only about 8 grams.
for a bbq rub, you're most likely using either granulated or brown sugar. if the recipe from bbqdad45 doesn't specify which one, i'd probably default to granulated sugar at 12.5g per tablespoon. it will probly be fine either way, since rubs are more forgiving than something like bread or a cake. this is why baking by weight is so much more accurate, but for this, you'll be okay.