var QNH = 29.92;\nvar OAT = 15;\nvar tempCorrection = (OAT – 15) * 120;\nvar pressureAltitude = (29.92 – QNH) * 1000 + tempCorrection;\ndocument.getElementById(\”pressureAltitude\”).value = pressureAltitude.toFixed(2);\n}\nfunction resetCalculator() {\ndocument.getElementById(\”QNH\”).value = \”29.92\”;\ndocument.getElementById(\”OAT\”).value = \”15\”;\ncalculatePressureAltitude();\n}\nfunction copyResults() {\nvar mainResult = document.getElementById(\”pressureAltitude\”).value;\nvar tempCorrection = (document.getElementById(\”OAT\”).value – 15) * 120;\nvar pressureAltitude = (29.92 – document.getElementById(\”QNH\”).value) * 1000 + tempCorrection;\nvar clipboardText = \”Pressure Altitude: \” + mainResult + \” ft\\n\”;\nclipboardText += \”Temperature Correction: \” + tempCorrection.toFixed(2) + \” ft\\n\”;\nclipboardText += \”Pressure Altitude Formula (Rule of Thumb): (29.92 – QNH) * 1000 + (OAT – 15) * 120\”;\nnavigator.clipboard.writeText(clipboardText).then(function() {\nvar button = document.querySelector(‘.btn-success’);\nbutton.innerHTML = ‘✓ Copied!’;\nsetTimeout(function() {\nbutton.innerHTML = ‘Copy Results’;\n}, 2000);\n}).catch(function() {\nalert(‘Failed to copy results’);\n});\n}\n// Setup event listeners\ndocument.addEventListener(‘DOMContentLoaded’, function() {\ncalculatePressureAltitude();\n});
Pressure Altitude Rule of Thumb Calculator
Quickly estimate pressure altitude using the standard aviation rule of thumb for non-critical flight planning. This calculator provides a fast approximation for pilot weather knowledge and preflight planning.
Enter the altimeter setting in inches of mercury (inHg). Standard sea level pressure is 29.92 inHg.
Enter the outside air temperature in degrees Celsius (°C).
How This Calculator Works
This calculator uses the standard aviation rule of thumb to quickly estimate pressure altitude. The formula is:
(29.92 – QNH) × 1000 + (OAT – 15) × 120
Where: QNH is the altimeter setting in inches of mercury (inHg), and OAT is the outside air temperature in degrees Celsius (°C). This approximation is particularly useful for quick in-flight checks and preflight planning when high precision is not required.
Pressure Altitude vs. Altimeter Setting
Common QNH Settings and Pressure Altitudes
| Altimeter Setting (inHg) | Pressure Altitude (ft) | Example |
|---|
Limitations of the Rule of Thumb
- Not suitable for IFR operations or instrument approaches where precision is critical
- Temperature correction is approximate and may not be accurate in extreme temperatures
- Best used for quick estimates rather than precise altimetry
- Does not account for non-standard atmosphere conditions beyond temperature
Safety Precautions
- Always verify altimeter settings with ATC or ATIS broadcasts
- Use certified altimeters for critical flight phases
- Cross-check with multiple sources when high accuracy is required
- Never rely solely on rule-of-thumb calculations for landing or takeoff