Calculate standard atmospheric pressure from geopotential altitude or estimate geopotential altitude from pressure in hPa, kPa, Pa, bar, atm, psi, inHg, and mmHg, with temperature and density.

Standard dry-air model, from −500 to 20,000 geopotential meters.

Use geopotential height, not uncorrected geometric elevation.

Leave empty for the standard 1013.25 hPa reference. A custom value scales this idealized model.

Atmospheric Pressure Formula

The calculator uses a layered dry-air standard-atmosphere approximation from −500 to 20,000 geopotential meters. Through 11 km, T = 288.15 − 0.0065H and P = P₀(T/288.15)^[g/(Rair × 0.0065)]. From 11 to 20 km, T = 216.65 K and P = P₁₁ exp[−g(H − 11000)/(Rair × 216.65)]. It uses g = 9.80665 m/s² and Rair = 287.05287 J/(kg·K). Geopotential height differs from geometric elevation, and actual weather may differ from this estimate. The image below is a separate constant-temperature (isothermal) approximation, shown for comparison.

  • Where P is the atmospheric pressure
  • P0 is the base level pressure at no height (101325 Pa)
  • H is the height (meters)
  • T is the temperature (K)
  • g is the acceleration due to gravity (9.8 m/s^2)
  • M is the molar mass of dry air (.028969 kg/mol)
  • R is the universal gas constant (8.3144626 J/(mol·K))

Atmospheric Pressure Definition

Atmospheric pressure refers to the force exerted by the Earth's atmosphere on objects within it. It is the weight of the air above a specific point, pushing down on the surface below.

This pressure results from the gravitational pull on the air molecules, causing them to be more tightly packed closer to the Earth's surface.

Atmospheric pressure plays a crucial role in various natural phenomena and human activities.

One significant impact of atmospheric pressure is on weather patterns. Differences in air pressure across regions create wind, which in turn influences the movement of weather systems. High-pressure areas tend to be associated with clear skies and calm weather, while low-pressure areas often indicate the presence of storms or precipitation.

Atmospheric Pressure Example

How to calculate atmospheric pressure?

  1. First, determine the height.

    Enter the geopotential altitude and select its unit.

  2. Next, choose the reference pressure.

    Leave the sea-level reference empty for 1013.25 hPa or enter a custom value.

  3. Finally, calculate the atmospheric pressure.

    Select the pressure result unit and Calculate; the layered equations above determine pressure, temperature and dry-air density.

FAQ

How does altitude affect atmospheric pressure?

As altitude increases, atmospheric pressure decreases. This is because at higher altitudes, the air is less dense and there are fewer air molecules to exert pressure.

Why is understanding atmospheric pressure important for weather prediction?

Atmospheric pressure is a key factor in weather systems. High and low-pressure areas influence wind patterns and precipitation, making it crucial for predicting weather conditions.

Can atmospheric pressure affect human health?

At high altitude, reduced barometric pressure lowers the partial pressure of inspired oxygen and can cause altitude illness. A pressure estimate alone cannot diagnose symptoms. See the CDC guidance on high-altitude travel.