Air Density Calculator

Air Density tells us how much does a certain volume of air weigh. It is given by the formula ρ = mass of air / volume. Density of Air is denoted by the symbol ρ and is used to measure the mass of air per unit volume. Dry air consists of gases such as nitrogen(78%), oxygen(21%) in major portions and the left over 1% includes various gases such as crabon dioxide, neon, helium, etc. However, the air will no longer be dry air till the water vapor appears.

Since Air is a mixture of gases it will not have constant density and the value depends on the air composition. Most of the Components have similar densities thus will not have much effect on the overall density. However, water vapor is an exception for it and higher the water vapor the lower the air density is.

In case of dry air, density at sea level at 59 °F (15 °C) and 14.7 psi (1013.25 hPa) is around 0.0765 lb/cu ft (1.225 kg/m³). On changing the humidity and altitude air density will alter too. As per the thumb rule, you will see a drop of 0.0022-0.0023 lb/cu ft (0.035-0.036 kg/m³) per 1000 ft of altitude change.

In order to determine the air density at a particular location you need to be well versed with several weather parameters and they are as such.

• Air Pressure: It is a barometric pressure expressed in units hPa.
• Air Temperature: It is simply the outside temperature measured in °C.
• Relative Humidity: Relative Humidity or Dew Point is the point in which the water vapor begins to condensate in °C.

The Procedure for calculating the air density is quite simple. Follow the simple guidelines listed below to determine the density of the air.

• Firstly, find out the saturation vapor pressure at a given temperature using the formula pΓéü = 6.1078 * 10^[7.5*T /(T + 237.3)] in which T is measured in Degree Celsius.
• Next find out the actual vapor pressure by multiplying saturation vapor pressure with relative humidity i.e. pv = pΓéü * RH
• Subtract the vapor pressure from total air pressure to find the dry air pressure we have the equation as pd = p - pv
• Substitute the known values in the formula ρ = (pd / (Rd * T)) + (pv / (Rv * T))
  • Where pd is the pressure of dry air and is measured in units are Pa
  • pv is the Water Vapor Pressre in units Pa
  • T is the Air Temperature in Kelvins
  • Rd is the specific gas constant for dry air and is equal to 287.058 J/(kg·K)
  • Rv is the specific gas constant for water vapor equal to 461.495 J/(kg·K)

Physicscalc.Com has got concepts like friction, acceleration due to gravity, water pressure, gravity, and many more along with their relevant calculators all one under one roof.

In the earlier sections you might have heard of the term Dry air. Do you want to know what exactly is dry air then look no further and go ahead with our further modules. Dry air is nothing but the air having low relative humidity and thus has a low dew point.

To better understand how temperature and pressure influence air density. Air Density Decreases as the air is heated. To learn how air changes with altitude check out the air density table for dry air provided below.

SI unit for Density is Kilogram Per Cubic Meter(Kg/m³). However, in certain scenarios it is better to use other units such as

• gram per cubic centimeter (g /c m³), 1 g/cm³ = 0.001 kg / m³
• kilogram per liter (kg / L), 1 kg/L = 1000 kg / m³
• gram per milliliter (g / mL), 1 g/mL = 1000 kg / m³

Based on the situation choose the units. Density of Air and its Imperial Units are as under

• pound per cubic feet (lb / cu ft);
• pound per cubic yard (lb / cu yd), 1 lb / cu yd ≈ 0.037 lb / cu ft;
• ounce per cubic inch (oz / cu in), 1 oz / cu in = 108 lb / cu ft;
• pound per gallon (US) (lb / US gal), 1 lb / US gal ≈ 7.48 lb / cu ft.

Since Temperature and Air Density varies from place to place you need to have standard air conditions. Have a look at the below sections to be able to know several standard reference pressures p₀ and temperatures T₀.

• As per International Union of Pure and Applied Chemistry(IUPAC): Standard Temperature and Pressure (STP), pΓéÇ = 10Γü╡ Pa, T = 0 °C;
• Institute of Standards and Technology (NIST): ISO 10780, pΓéÇ = 1 atm, T = 0 °C;
• International Civil Aviation Organization (ICAO): International Standard Atmosphere (ISA), pΓéÇ = 1 atm, T = 15 °C;
• United States Environmental Protection Agency (EPA): Normal Temperature and Pressure (NTP), pΓéÇ = 1 atm, T = 20 °C;

• International Union of Pure and Applied Chemistry: Standard Ambient Temperature and Pressure (SATP), pΓéÇ = 10Γü╡ Pa, T = 25 °C;

Air Pressure is a Physical Property of Gas that tells us how much strength it has while acting on surroundings. As per Kinetic Theory of Gases, Molecules of Gas will be in constant motion and has a velocity that depends on thermal energy. Particles collide with each other and hit the walls of the container and exerts a tiny force on them. By the time number of enclosed molecules reach the magnitude of Avogadro's Number ~10²³ the total force becomes significant and measurable and this is the pressure.

Relative Humidity RH is the ratio of partial pressure of water vapor to the equilibrium vapor pressure of water at a given temperature. p_total = p_NΓéé + p_OΓéé + p_Ar + p_HΓééO + ... Relative Humidity ranges between 0% to 100% and 0% means dry air and 100% means air is completely saturated with water vapor.

Dew Point is a physical quantity and is relted to humidity of air. It is the temperature at which the water vapor in air reaches its saturation state. Due Point can be found easily using the formula DP = 243.12 * α / (17.62 - α) in which α depends on the relative humidity RH and Temperature T. α = ln(RH/100) + 17.62 * T / (243.12 + T)

1. What is meant by Air Density?

Air Density tells us how much does a certain volume of air weigh.

2. What affects the density of air?

The air density depends on factors such as temperature, pressure, how much water vapor is in air.

3. What is the formula for air density?

The Formula for Air Density is ρ = (pd / (Rd * T)) + (pv / (Rv * T))

4. What is the SI unit of Density of Air?

The SI unit of Air Density is Kilogram Per Cubic Meter(kg / m³).