Weight Units in Cooking vs Pharmacy
How grams, ounces, and grains are used differently in cooking, pharmacy, and precious metals.
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Weight Units in Cooking vs Pharmacy The word "ounce" means three different things depending on context: a cooking ounce (28.35 g), a troy ounce for precious metals (31.10 g), and an apothecary ounce for historical pharmacy (also 31.10 g). Using the wrong one can matter enormously. --- The Four Weight Systems | System | Primary use | Base units | |--------|------------|-----------| | Metric (SI) | Science, medicine, most cooking | gram, kilogram | | Avoirdupois | Everyday weight, cooking, commerce | ounce (28.35 g), pound (453.6 g) | | Troy | Precious metals, gemstones | troy ounce (31.10 g), troy pound | | Apothecary | Historical pharmacy | grain, scruple, dram, apothecary ounce | Avoirdupois: Everyday and Cooking Weight The avoirdupois system (from French avoir du poids — "to have…
Frequently Asked Questions
What is a troy ounce?
A troy ounce is a unit of weight for precious metals (gold, silver, platinum) and gemstones: 1 troy ounce = 31.1035 grams. It is heavier than the avoirdupois ounce (28.3495 g) used in cooking and everyday weight. Gold prices are quoted per troy ounce on commodity markets worldwide. The troy system also includes troy pounds (12 troy ounces, not 16).
How are weight units different in pharmacy?
Modern pharmacy uses metric units — milligrams (mg), grams (g), and micrograms (μg or mcg) — for drug dosing and compounding. However, older pharmaceutical systems (apothecary and avoirdupois) still appear in historical texts and some traditional contexts. The apothecary grain (gr) = 64.8 mg is still seen in aspirin dosing (5 gr = 325 mg) in the US.
What is a grain in weight measurement?
A grain (gr) is one of the oldest weight units, originally defined as the weight of a single grain of barley or wheat. It equals 64.7989 mg (approximately 65 mg). The grain is still used in US pharmacology (aspirin dose: 5 grains = 325 mg), in ballistics for bullet and powder weights, and in traditional archery for arrow weight. 1 avoirdupois ounce = 437.5 grains; 1 troy ounce = 480 grains.
How are precious metals measured in ounces?
Precious metals (gold, silver, platinum, palladium) are universally priced in troy ounces on international commodity markets. 1 troy ounce = 31.1035 g = 480 grains. A troy pound = 12 troy ounces = 373.24 g. This differs from the avoirdupois pound (16 oz = 453.6 g). When you see 'gold at $2,000/oz,' that's per troy ounce.
What is an apothecary unit?
The apothecary system is an old pharmaceutical weight system that predates modern metric pharmacy. Its units include: grain (gr) = 64.8 mg, scruple (℈) = 20 grains = 1.3 g, dram (ʒ) = 3 scruples = 3.89 g, ounce (℥) = 8 drams = 31.1 g, pound = 12 ounces = 373 g. The apothecary ounce is coincidentally the same size as a troy ounce. Most countries have fully replaced the apothecary system with metric units.
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