Engineering units
The Alphabet of Engineering
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Engineering calculations need clear, consistent units. The International System of Units (SI) is used in technical drawings, calculations and manufacturing. Always state the unit and convert before combining quantities.
Seven SI base units
| Quantity | Unit | Symbol |
|---|---|---|
| Length | metre | m |
| Mass | kilogram | kg |
| Time | second | s |
| Electric current | ampere | A |
| Thermodynamic temperature | kelvin | K |
| Luminous intensity | candela | cd |
| Amount of substance | mole | mol |
Derived quantities
Force: F = m × a; 1 N = 1 kg·m/s². Work: W = F × s; 1 J = 1 N·m. Power: P = W/t; 1 W = 1 J/s. Pressure: p = F/A; 1 Pa = 1 N/m².
Useful conversions
1 kgf ≈ 9.80665 N · 1 kW ≈ 1.341 hp · 1 in = 25.4 mm · 1 bar = 100 kPa. Temperature: K = °C + 273.15.
Mass and force are different quantities: a 1 kg mass weighs about 9.81 N under standard Earth gravity. Check dimensions, symbols and unit prefixes in every calculation.