Bakings general rules from Joyofbaking

BAKING POWDER AND SODA:
1 teaspoon = 5 grams

The general rule of thumb for amount of baking powder in recipes: 1 to 2 teaspoons (5-10 grams) of baking powder leavens 1 cup (140 grams) of flour.  The amount will depend on the ingredients and how they are mixed.

BUTTER:
1 cup = 226 grams
1 tablespoon = 14 grams

Note: Can substitute 8 ounces (226 grams) of lightly salted butter for 8 ounces unsalted butter, but remove 1/2 teaspoon (3.5 grams) salt from recipe.

TIP:  Room temperature butter means the butter should only give slightly when pressed with index finger.

CREAMS:
Heavy cream (30-40% butterfat):
1 cup (240 ml) = 232 grams
Milk, Buttermilk, Sour Cream, and Half-and-Half:
1 cup (240 ml) = 242 grams

EGGS:
Freshness Test:  Place an egg in water mixed with a little salt. If the egg is fresh it will sink. The quicker or farther it sinks, the fresher it is. If the egg floats, it has spoiled.
TIP:  Cold eggs are easier to separate than warm eggs.

TIP:  To achieve maximum volume when beating eggs, have them at room temperature.
TIP:  Always use large eggs in recipes where egg size is not given.