Quick reference for technical units
| Quantity | SI unit | Common conversion | Everyday example |
|---|---|---|---|
| Density | kg/m³ | 1 g/cm³ = 1,000 kg/m³ | Water is about 1,000 kg/m³; steel about 7,850 kg/m³ |
| Force | newton (N) | 1 lbf = 4.448 N; 1 kgf = 9.807 N | Holding a 1 kg bag takes about 9.8 N |
| Torque | newton metre (N·m) | 1 lbf·ft = 1.356 N·m | Wheel nuts on many cars are tightened to roughly 80-140 N·m (check the handbook) |
| Dynamic viscosity | pascal second (Pa·s) | 1 cP = 1 mPa·s | Water at 20 °C is about 1 mPa·s |
| Momentum | kg·m/s | 1 N·s = 1 kg·m/s | A 70 kg runner at 5 m/s has 350 kg·m/s |
These quantities are derived from the SI base units: a newton is 1 kg·m/s², a pascal is 1 N/m², and a newton metre of torque is a force of one newton acting one metre from the axis. Writing out the base units is a quick way to check that a conversion makes sense: torque in N·m and energy in joules have the same base units but describe different things, so they should not be converted into each other.