US Customary vs. Metric System in Cooking
Understand the key differences between US volume measurements and metric weight, and why switching to weight makes you a better baker.
US Customary vs. Metric: What's the Difference?
The United States uses the Customary system (cups, ounces, teaspoons), while most of the world uses the Metric system (grams, milliliters). Beyond the names, the deeper difference is what these units measure: volume versus weight.
Volume vs. Weight: The Core Distinction
- US Customary: Primarily measures volume (how much space an ingredient occupies).
- Metric: Primarily measures weight (how heavy an ingredient is).
This is why converting tsp to grams is complex: you are converting space into weight, which requires knowing the ingredient's density.
Why Volume Measurements Are Unreliable
Measuring flour by volume is notoriously inaccurate. If you scoop flour straight from the bag it compresses, and 1 cup of scooped flour can weigh 150 grams. If you sift and gently spoon it in, the same cup might weigh only 120 grams. That 30-gram difference changes your cookies from chewy to dry.
The same problem affects tsp to ml conversions less, because liquids measured by volume are consistent. But dry ingredients measured in cups and teaspoons vary with how they're packed, sifted, and scooped.
Why Metric Weight Wins for Baking
120 grams of flour is always 120 grams, no matter how it was scooped, sifted, or packed. That consistency is why professional bakeries measure everything by weight.
It also makes scaling recipes trivial. To make 1.5x a recipe, multiply 120 g by 1.5. Doing the same with "3/4 of a cup" is fiddly and error-prone.
When Volume is Fine: Liquids
For liquids, volume measurement works because both systems measure the same physical property. Converting teaspoon to ml is a clean, fixed equation (1 tsp = 5 mL) with no density involved. You can use our teaspoons to milliliters converter for that.
A Simple Rule
- Liquids: cups, fluid ounces, teaspoons, and milliliters all work reasonably well together.
- Dry ingredients (flour, sugar, salt): use weight (grams) for reliability.
- Small amounts (spices, leaveners): use teaspoons for convenience, but know their gram weight.
As the culinary world globalizes, adopting a kitchen scale and learning metric weights will make you a far better, more versatile cook.