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Core engineering quantities
Reference factors
| Quantity | SI | US customary | Factor |
|---|---|---|---|
| Force | newton (N) | pound-force (lbf) | 1 lbf = 4.448 N |
| Pressure / stress | pascal (Pa) | psi | 1 psi = 6,895 Pa |
| Torque | N·m | ft·lb | 1 ft·lb = 1.356 N·m |
| Energy | joule (J) | BTU | 1 BTU = 1,055 J |
| Power | watt (W) | horsepower (hp) | 1 hp = 745.7 W |
| Flow | m³/s | gpm (US) | 1 gpm = 6.31×10⁻⁵ m³/s |
Drawing & spec conventions
- Title block must list primary units (SI or US) and tolerance system
- Bilingual drawings show metric primary with imperial in brackets, e.g. 50 (1.97")
- Avoid units without prefixes for very large/small numbers — use kPa not Pa for line pressures
Why this matters: Mars Climate Orbiter
The thruster performance data tables were delivered in pound-force seconds while the navigation software expected newton-seconds — the spacecraft entered Mars' atmosphere at the wrong altitude and was destroyed.
Convert engineering units
PSI ↔ kPa
PSI (psi)
Kilopascal (kPa)
Press / to focus
| Unit | 1 psi equals |
|---|---|
| Pascal (Pa) | 6,894.76 |
| Kilopascal (kPa) | 6.89476 |
| Megapascal (MPa) | 0.00689476 |
| Bar (bar) | 0.0689476 |
| PSI (psi) | 1 |
| Atmosphere (atm) | 0.068046 |
| Torr (Torr) | 51.7151 |
| mmHg (mmHg) | 51.7151 |
Related converters
The tools mentioned in this guide — one tap away.
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