Units of Measure by weight and by volume

US fluid Units of Measure (by volume/capacity)
drop0.03850720011416 drops = 1/8 teaspoon
teaspoon4.9289216145863 teaspoons = 1 tablespoon
tablespoon14.7867648437591 tablespoon = 3 teaspoons
ounce (fluid)29.5735296875171 cup = 8 ounces
cup236.5882375001361 cup = 16 tablespoons
pint473.1764730000001 pint = 2 cups = 16 fluid ounces
quart946.3529500005441 quart = 4 cups
liter1000.0000000000001 liter = 0.264 gallons = 61.024 cubic inches
gallon3785.4117800000001 gallon = 128 fluid ounces
Dry Units of Measure (by weight)
ounce (dry)28.349523100000 
pound453.5923696000001 pound = 16 dry ounces
pint (dry)550.6104713575001 dry pint = 33.6003125 cubic inches
quart (dry)1101.2210000000001 dry quart = 67.2006 cubic inches
gallon (dry)4404.8837708600001 dry gallon = one-eighth of a bushel
peck8809.7680000000001 Peck = 8 Dry Quarts = 537.6 cubic inches

Measurements are based on either weight, or volume (capacity). There is no specific conversion between weight and volume unless you know the density of the ingredient. However, water, at 4 °C, is often used as a standard to derive the weight of a volume specification. For example, one cup of water (at 4 °C) weighs 236.588 grams. A cup of popcorn, of course, weighs much less (8 grams). Here is the USDA list of Food Item Densities for one cup of selected food items.

Both liquid measure and dry measure have the same volume.

For the most precise measurements, weigh all ingredients with a scale.