Cheat sheet
Air density & power loss
Every number below comes from the same formula as the density-altitude calculator, so a printed sheet and the tool can never disagree. Read your temperature and pressure, and the cell is the power a naturally aspirated engine has left compared with a standard day.
| Temp | 98 kPa | 100 kPa | 101.3 kPa | 103 kPa |
|---|---|---|---|---|
| 5 °C | 100.0% | 102.1% | 103.4% | 105.1% |
| 10 °C | 98.2% | 100.2% | 101.5% | 103.2% |
| 15 °C | 96.4% | 98.4% | 99.7% | 101.3% |
| 20 °C | 94.6% | 96.6% | 97.8% | 99.5% |
| 25 °C | 92.9% | 94.8% | 96.1% | 97.7% |
| 30 °C | 91.2% | 93.1% | 94.3% | 95.9% |
| 35 °C | 89.5% | 91.3% | 92.5% | 94.1% |
| 40 °C | 87.7% | 89.5% | 90.7% | 92.3% |
101.3 kPa is standard sea-level pressure; 98 kPa is roughly 280 m of elevation or a deep low-pressure system. Boosted engines lose far less than this — the compressor makes up the difference until it runs out of map.
| Change | Density altitude | NA power |
|---|---|---|
| 10 °C hotter | +1161 ft (354 m) | 3.4 pts |
| 1 kPa lower pressure | +339 ft (103 m) | 1.0 pts |
| dry → saturated at 30 °C | +538 ft (164 m) | 1.5 pts |
Measured by moving one input at a time from a standard day (15 °C, 101.3 kPa, dry). Humidity matters least, but it is not nothing — water vapour displaces oxygen.