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Glossary
International System of Units (SI)
SI means the International System of Units (from the French Système international d’unités). It’s the modern, globally agreed “rulebook” for measurement units used in science and industry—so when everyone sticks to SI, a meter or a newton means the same thing in every plant, lab, and drawing package.
In industrial engineering, SI is the backbone for consistent calculations and specs. The core SI base units include things like the meter (m) for length, kilogram (kg) for mass, second (s) for time, ampere (A) for electric current, kelvin (K) for temperature, mole (mol) for amount of substance, and candela (cd) for luminous intensity. From those, you get derived units you use constantly—newton (N) for force, pascal (Pa) for pressure, joule (J) for energy, and watt (W) for power.
One nuance that trips people up: SI is a system, not just “metric.” For example, °C is accepted for use with SI, but the base SI temperature unit is K. So a spec might be written in °C for practicality, while calculations use K when absolute temperature is needed.