Perhaps the best way is to describe it is "inconsistently".
Most scientists use the international system and when they don't, they have disasters like the one that trashed NASA's Mars Climate Orbiter!
It's used for all measurement in most of the world. This is also called the metric system; SI is the French abbreviation for System International - and it's used internationally. The US is the most obvious country that doesn't use metric units for everyday measure, although these units are used in science and medicine among others.
Système International, the international system of units since 1960.Includes everyday measurements like grams, litres and metres. Widely used as the established system of measurement throughout the world with the notable exception of the US.
Centi (= 10-2) is an accepted prefix in the International System of Units (SI).
the international system of units (also called standards) are kept at the International Bureau of Weights and Measures. JENNIFER A.
In the United States we use US, or Customary Units, like inches, feet, etc. In most other countries they use the international system, or SI, units, like meters, kilometers, etc. In the SI system conversions are made in multiples of 10, making it simpler
Much the same as many of us in the UK still do. We are used to the Imperial system for everyday things; but the legally-recognised international system for trade, and the international system for science, is the Metric, or more properly, its derivative the SI, system. (System Internationale).
US customary units
The answer here us weight. The gram is the International system of units (SI) designated unit for weight.
Newton in SI Pounds in US Customery units system
british system
The international system of units is practically legal in all the countries; but some countries as United States, United Kingdom and the old colonies of US and UK refuse this system.
As I remember from grade school back in the 1960's I believe it was called: "Units and Standards" We refer to the U.S. measurement system today as the "Standard Measurement," "US Standard," "English Units," "US Customary Units," and "Imperial Units."