The seven SI base units: quantities, names and symbols

Match each unit to its quantity

BIPM, the international institution coordinating the SI, lists second (s) for time, metre (m) for length and kilogram (kg) for mass. The other four are ampere (A) for electric current, kelvin (K) for thermodynamic temperature, mole (mol) for amount of substance and candela (cd) for luminous intensity.

A unit name, its symbol and the quantity it measures are separate items. A good GK answer preserves all three rather than guessing a quantity from how familiar a word sounds.

Base units and derived units

The SI base-unit page explains that other SI units can be derived by combining powers of base units. For example, the classroom expression metres per second combines length and time to describe speed. This example illustrates the relationship without introducing a new base quantity.

BIPM states that the modern SI defines units through fixed numerical values of defining constants. The definitions of four base units changed in the 2018 revision, while the revised system took effect in 2019. This is historical system information, not an announcement of a new revision today.

An original practice exercise

Take a blank sheet and write the seven quantities in one column. Fill in the unit names, cover them, then add the symbols from memory. Reverse the exercise by starting with symbols and asking what they measure. The aim is to build accurate pairs rather than memorise an unexplained list.

Check case carefully: A and K are uppercase, while s, m, kg, mol and cd are lowercase. When solving a numerical question, write the unit alongside the number and see whether it matches the requested quantity. This prevents a calculation with a plausible number from being accepted when it answers the wrong measurement question.

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