Metric volume vs Imperial volume: base 10 vs base 2



I grew up with metric, so I have a natural bias. Metric seems orderly in it’s progressions and Imperial seems utterly inconsistent. Imagine my surprise at the apparent order in US volumes revealed at Flowing Data’s Baking units demystified post. It dawned on me that the order is a question of base:

  • Metric volumes are base-10
  • US Imperial volumes are base-2

Specifically

  • 1 gallon = 4 quarts
  • 1 quart = 2 pints
  • 1 quart = 4 cups
  • 1 cup = 8 fluid oz
  • 1 fluid oz = 2 tablespoons

I was quite excited that I’d just missed a fundamental mapping and incorrectly judged the system and then I looked at the Wikipedia Cup (unit) page and gave up all hope:

  • US customary cups vs US legal cups vs UK cups
  • US customary pints vs Imperial pints
  • International teaspoons vs Australian teaspoons

It seems the Imperial orderly progressions are limited to the base-2 US customary baking volumes. Oh well. And why do we measure ingredients by volume anyway?

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