Derived SI units are formed from combinations of the seven base SI units and are used to describe physical quantities such as force, energy, pressure, and electrical properties. This table provides a quick engineering reference for unit names, symbols, and their fundamental derivations.
| Physical quantity | Name | Symbol | Derivation |
|---|---|---|---|
| force | newton | N | kg·m / s2 |
| power | watt | W | kg·m2 / s3 |
| energy | joule | J | kg·m2 / s2 |
| pressure | pascal | Pa | kg / (m·s2) |
| electric charge | coulomb | C | A·s |
| electric potential difference | volt | V | kg·m2 / (A·s3) |
| electric resistance | ohm | Ω | kg·m2 / (A2·s3) |
| electric conductance | siemens | S | A2·s3 / (kg·m2) |
| electric capacitance | farad | F | A2·s4 / (kg·m2) |
| magnetic flux | weber | Wb | kg·m2 / (A·s2) |
| inductance | henry | H | kg·m2 / (A2·s2) |
| magnetic flux density | tesla | T | kg / (A·s2) |
| luminous flux | lumen | lm | cd·sr |
| illuminance | lux | lx | cd·sr / m2 |
| absorbed dose | gray | Gy | m2 / s2 |
| activity | becquerel | Bq | 1 / s |
| dose equivalent | sievert | Sv | m2 / s2 |
| acceleration | - | - | m / s2 |
| angular velocity | - | - | rad / s |
| area | - | - | m2 |
| current density | - | - | A / m2 |
| density | - | - | kg / m3 |
| dynamic viscosity | pascal second | - | Pa·s |
| electric charge density | coulomb / m2 | - | C / m2 |
| electric field strength | volt / metre | - | V / m |
| energy density | joule / m3 | - | J / m3 |
| heat capacity | joule / kelvin | - | J / K |
| heat flux density | watt / m2 | - | W / m2 |
| kinematic viscosity | m2 / s | - | m2 / s |
| luminance | candela / m2 | - | cd / m2 |
| magnetic field strength | ampere / metre | - | A / m |
Derived SI units are fundamental in engineering calculations and are obtained by combining base units such as metre (m), kilogram (kg), second (s), and ampere (A). Understanding these relationships allows engineers to verify equations, check dimensional consistency, and convert between unit systems.
For practical engineering design, these units are used in fields such as mechanics, thermodynamics, fluid dynamics, and electrical engineering.