Calculator
Boost Pressure Converter
Convert turbo and supercharger boost between bar, psi and kPa, and see the absolute pressure and pressure ratio a compressor map needs.
2.05 bar absolute in the intake: about 2.0 times the air pressure the engine would breathe on its own.
Gauge pressure, absolute pressure and pressure ratio
A boost gauge shows gauge pressure: how far the intake is above the outside air. 1 bar of boost means about 2 bar absolute in the manifold, because the atmosphere already supplies 1.013 bar at sea level. Engine management (MAP sensors) and many European spec sheets work in absolute pressure.
Turbo compressor maps use the pressure ratio: absolute outlet pressure divided by inlet pressure. 1 bar of boost is a ratio of about 2.0; a stock turbo petrol engine runs 1.8-2.5, and the same boost needs a higher ratio at altitude, where the inlet air is thinner.
Formulas
- 1 bar = 14.504 psi = 100 kPa
- Absolute = boost + 1.013 bar (sea level)
- Pressure ratio = absolute ÷ 1.013 bar
Conversion table
| bar | psi | kPa | Pressure ratio |
|---|---|---|---|
| 0.3 bar | 4.4 psi | 30 kPa | 1.30 |
| 0.5 bar | 7.3 psi | 50 kPa | 1.49 |
| 0.8 bar | 11.6 psi | 80 kPa | 1.79 |
| 1.0 bar | 14.5 psi | 100 kPa | 1.99 |
| 1.2 bar | 17.4 psi | 120 kPa | 2.18 |
| 1.5 bar | 21.8 psi | 150 kPa | 2.48 |
| 1.8 bar | 26.1 psi | 180 kPa | 2.78 |
| 2.0 bar | 29.0 psi | 200 kPa | 2.97 |
| 2.5 bar | 36.3 psi | 250 kPa | 3.47 |
| 3.0 bar | 43.5 psi | 300 kPa | 3.96 |
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