Altitude to Atmospheric Pressure Calculator
Calculate atmospheric pressure at different altitudes and understand its effects.
About Altitude Pressure
Atmospheric pressure decreases with altitude following the barometric formula. This calculator helps you understand:
- Pressure changes at different altitudes
- Effects on human physiology
- Impact on equipment and machinery
- Aviation and mountaineering considerations
Altitude Zones
- Sea Level: Normal atmospheric conditions
- Low Altitude: Slight pressure decrease, minimal effects
- Medium Altitude: Moderate pressure decrease, may affect breathing
- High Altitude: Significant pressure decrease, requires acclimatization
- Very High Altitude: Severe pressure decrease, dangerous without preparation
- Extreme Altitude: Extreme conditions, life-threatening without equipment
How Altitude and Atmospheric Pressure Are Related
An altitude pressure converter estimates the atmospheric pressure at a given height above sea level, or works backward from a measured pressure to an approximate altitude. The link between the two is direct: as you climb, there is less air above you pressing down, so the pressure falls. At sea level the standard pressure is about 1013.25 hPa (101,325 Pa, or 29.92 inHg), and it drops steadily as altitude increases.
The decrease is not linear. Pressure falls fastest near the ground and more slowly at high altitude, because air is compressible and most of the atmosphere's mass sits in the lowest layers. Roughly half of all air molecules lie below about 5,500 meters, which is why pressure at that height is close to half of sea-level pressure.
- Higher altitude means lower pressure.
- The relationship is exponential, not a straight line.
- Temperature affects the result, so standard-atmosphere values are approximations.
The Barometric Formula
The most common way to convert altitude to pressure is the barometric formula based on the International Standard Atmosphere within the troposphere (up to about 11,000 m). It accounts for the temperature lapse rate, the steady cooling of air with height:
P = P₀ × (1 − (L × h) / T₀) ^ (g × M / (R × L))
Where the standard constants are:
- P₀ = sea-level pressure = 101,325 Pa
- T₀ = sea-level temperature = 288.15 K (15 °C)
- L = temperature lapse rate = 0.0065 K/m
- h = altitude in meters
- g = gravity = 9.80665 m/s²
- M = molar mass of air = 0.0289644 kg/mol
- R = universal gas constant = 8.31446 J/(mol·K)
The exponent g×M / (R×L) works out to about 5.255. A simpler approximation for quick mental math is P ≈ P₀ × e^(−h / 8400), which treats 8,400 m as the scale height where pressure falls to about 37% of its sea-level value.
Altitude vs Pressure Table
The table below shows approximate standard-atmosphere pressure at several altitudes. Values use the barometric formula and round for readability. Use them as a reference when calibrating instruments, planning a hike or checking aircraft and weather data.
| Altitude | Pressure (hPa) | Pressure (inHg) | % of sea level |
|---|---|---|---|
| 0 m (sea level) | 1013 | 29.92 | 100% |
| 500 m | 955 | 28.20 | 94% |
| 1,000 m | 899 | 26.55 | 89% |
| 2,000 m | 795 | 23.48 | 78% |
| 3,000 m | 701 | 20.70 | 69% |
| 5,500 m | 505 | 14.92 | 50% |
| 8,848 m (Everest) | 314 | 9.28 | 31% |
For example, at 3,000 m the formula gives roughly 701 hPa, about 69% of sea-level pressure, which is why many people notice thinner air and lower oxygen at mountain elevations.
Limits and Practical Uses
These conversions assume the International Standard Atmosphere, a model with fixed temperature and lapse rate. Real conditions vary: a warm air mass, a passing storm or local weather can shift the actual pressure by 20 to 30 hPa from the standard value. So treat converter output as a close estimate rather than an exact reading.
The formula above is valid up to about 11,000 m, the top of the troposphere. Above that the temperature stops falling at the standard rate and a different equation applies. Within its range the barometric formula is widely used in aviation altimetry, where altimeters convert measured pressure into displayed altitude, as well as in weather forecasting, hiking and mountaineering, and engineering tasks like sizing pumps or calibrating sensors. If you need altitude from pressure instead, simply rearrange the formula to solve for h.
Frequently Asked Questions
The higher you go, the less air sits above you to press down, so pressure falls. Because air is compressible and most of its mass is near the ground, pressure drops fastest at low altitudes and more slowly higher up.
Standard sea-level pressure is 1013.25 hPa, equal to 101,325 Pa, 29.92 inHg or 1 atmosphere. This is the reference point used in the barometric formula.
Atmospheric pressure reaches about 50% of sea-level value near 5,500 meters (around 18,000 feet). This is also roughly where half of all air molecules lie below you.
It is accurate for the standard atmosphere up to about 11,000 m, but real weather, temperature and humidity can shift actual pressure by 20 to 30 hPa, so results are reliable estimates rather than exact measurements.
Yes. Rearrange the barometric formula to solve for height h. Altimeters do exactly this, converting measured pressure into displayed altitude, though they must be calibrated to local conditions for accuracy.
Yes. The formula uses a standard temperature and lapse rate, so warmer or colder air than the model assumes will change the true pressure at a given height. That is why the result is a standard-atmosphere approximation.