The modern metric system—known as the International System of Units, or SI—is a model of consistency and logic. But in some cases, the logic seems to break down.

In this article, we’ll explore some of these quirks and why they (mostly) make sense at the end of the day (or approximately 86,400 seconds, as we might say at NIST).

1. Why is the kilogram (1,000 grams) a basic unit of measurement instead of just the gram?

In the metric system, we express quantities using individual units, such as length in meters and time in seconds. But the unit of mass is a kilogram—1,000 grams (kilo = thousand).

Why isn’t the gram itself a base unit in the SI? Well, for starters, it was once hard to make objects that were exactly one gram. Kilograms, which are equal to about 2.2 pounds, were much easier to make accurately and more useful in day-to-day trade.

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