The Gause on a Compressed Air Tank Reads 43.2 Lb In2. What Is the Pressure in Atm Answer

Air Density Computer

Created by Dominik Czernia , PhD candidate and Bogna Szyk

Reviewed by

Małgorzata Koperska , MD and Jack Bowater

Terminal updated:

Feb 15, 2022

Table of contents:

• What is the density of air? - density of air at sea level
• How to calculate the air density?
• Air density definition - what is the density of air formula?
• Air density table - the density of dry air
• Density of air in kg / m³ and density of air in English units
• Standard air density
• What is air force per unit area?
• What is relative humidity?
• What is the dew point?

Use this air density calculator to instantly observe how tightly packed an object'due south molecules are, allowing you to gauge the ρ (air density) parameter basing on the local temperature and force per unit area weather condition. This value is vital for many farther calculations, such every bit determining the aerodynamic drag forces or the functioning of wind turbines. Continue reading to get a better understanding of the relationship between the local conditions and ρ, and learn what air density levels yous can look in various regions.

The density of air depends on many factors and tin can vary in different places. It mainly changes with temperature, relative humidity, pressure and hence with altitude (take a expect on the air density table below). The air pressure can be related to the weight of the air over a given location. It is easy to imagine that the higher you lot stand up, the less air is above you and the pressure is lower (check out our definition of force per unit area!). Therefore, air pressure decreases with increasing altitude. In the following text, you will find out what is the air density at sea level and the standard air density.

You might also want to check out our speed of sound calculator which is a tool that helps you calculate the speed of audio in dry out air and water at any temperature.

What is the density of air? - density of air at sea level

The density of air is normally denoted past the Greek alphabetic character ρ, and it measures the mass of air per unit volume (due east.g. g / thou³). Dry out air generally consists of nitrogen (~78 %) and oxygen (~21 %). The remaining 1 % contains many dissimilar gases, amidst others, argon, carbon dioxide, neon or helium. However, the air will cease to be dry air when water vapor appears.

As a mixture of gases, air doesn't accept a constant density; this value depends largely on air limerick. Almost components take like densities and don't influence the overall density in a substantial fashion. One exceptions is h2o vapor; the more than h2o vapor in the air, the lower its density.

For dry air, its density at ocean level at 59 °F (xv °C) and 14.seven psi (1013.25 hPa) (mean sea-level pressure), is approximately 0.0765 lb/cu ft (1.225 kg/m³). If you change the air temperature, humidity, or the altitude (and hence the pressure), the air density will change, as well. As a rule of thumb, y'all can expect a drop of 0.0022-0.0023 lb/cu ft (0.035-0.036 kg/thou³) per thousand ft of distance change.

How to calculate the air density?

To detect the air density at whatsoever given location, you will demand some basic weather parameters. You tin can usually notice them on your local conditions stations website.

• Air pressure level: the barometric pressure expressed in hPa. If the analyzed location is at a high distance, you can use our air pressure at altitude calculator to found a more than authentic value for this parameter.
• Air temperature: simply, the exterior temperature in °C.
• Relative humidity or dew point: our air density calculator is able to use one of these values to compute the other or y'all can also use our dew indicate figurer. Dew betoken is the temperature below which the water vapor starts to condensate, in °C.

The method of finding the air density is quite unproblematic. You have to dissever the pressure exerted by the air into two partial pressures: of the dry air and of the water vapor. Combining these 2 values gives y'all the desired parameter.

1. Calculate the saturation vapor pressure at given temperature T using the formula p₁ = 6.1078 * 10^[7.five*T /(T + 237.3)], where T is measured in degrees Celsius. Saturation vapor pressure is the vapor force per unit area at 100% relative humidity (our reckoner uses a more accurate, but also style more complicated equation that we didn't want to show hither. If you are curious, cheque "Role ESW(T)" in the provided link).
2. Detect the actual vapor pressure level, multiplying the saturation vapor force per unit area by the relative humidity: pv = p₁ * RH.
3. Subtract the vapor pressure from the total air pressure to detect the pressure of dry out air: pd = p - pv.
4. Input the calculated values into the following formula:

ρ = (pd / (Rd * T)) + (pv / (Rv * T))

where:

• pd is the pressure of dry out air in Pa,
• pv is the water vapor pressure in Pa,
• T is the air temperature in Kelvins,
• Rd is the specific gas constant for dry air equal to 287.058 J/(kg·K), and
• Rv is the specific gas constant for h2o vapor equal to 461.495 J/(kg·K).

Air density definition - what is the density of air formula?

The basic definition of air density is very similar to the general definition of density. It tells u.s.a. how much does a certain volume of air counterbalance. We can express it with the following density of air formula:

ρ = mass of air / volume

From the in a higher place equation, you may suspect that the density of air is a constant value that describes a certain gas property. However, the density of every matter (solids, liquids, gases) depends, stronger or weaker, not only on the chemic composition of the substance only also on the external conditions like pressure and temperature.

Because of these dependencies and the fact that the Earth's atmosphere contains various gases (mostly nitrogen, oxygen, argon and water vapor) the air density definition needs to exist further expanded. A proper modification has been made in our air density estimator with the density of air formula shown in the section chosen "How to calculate the air density?".

By the way, we would like to bring up an interesting point. What practise you think? Is moist air heavier or lighter than dry out air? The right answer may non be every bit intuitive equally you tin think at outset. In fact, the more water vapor nosotros add to the air, the less dense information technology becomes! You may observe this hard to believe, simply we will try to convince with some few logical argumentations.

Commencement of all, we need to refer to the Avogadro's law which states that

equal volumes of all gases, at the same temperature and pressure, have the same number of molecules.

Imagine that you put dry air into a container of fixed volume, temperature and pressure level. The perfectly dry out air is equanimous of:

• 78% molecules of nitrogen Due north₂ that has ii N atoms with atomic weight 14 u (total weight is 28 u),
• 21% molecules of oxygen O₂ that has two O atoms with atomic weight xvi u (total weight is 32 u), and
• i% molecules of argon Ar (Ar has 1 atom with diminutive weight 39.viii u).

Annotation that every molecule listed is heavier that or equal to 18 u. Now, let's add some h2o vapor molecules to the gas with the total diminutive weight of 18 u (H₂O - two atoms of hydrogen 1 u and one oxygen 16 u). According to Avogadro's police force, the total number of molecules remains the same in the container under the same weather (volume, pressure, temperature). It ways that water vapor molecules accept to supervene upon nitrogen, oxygen or argon. Because molecules of H₂O are lighter than the other gases, the total mass of the gas decreases, decreasing the density of the air too.

Air density table - the density of dry air

In the previous sections, we used the term dry out air a couple of times. However, what does it actually mean? There are two definitions:

• The most common definition is air without any h2o vapor inside it. The air in the atmosphere is never perfectly dry since it ever contains some water, though.
• Some other, more realistic definition says that dry air is air with low relative humidity and thus with a low dew point.

A well-known approximation of dew betoken is a logarithmic role of relative humidity. Every bit yous may know, when the part of a logarithm approaches zero, its value goes to minus infinity. Therefore, a dew point doesn't exist for the zero relative humidity. Even so, you can still calculate what is the density of dry out air with our air density calculator! Merely select dry air in the "air type" field, where we have ignored dew point/relative humidity in the computations.

For a better understanding of how temperature and pressure influence air density, let's focus on a case of dry air. It contains more often than not molecules of nitrogen and oxygen that are moving around at incredible speeds. Utilise our particles velocity calculator to come across how fast they can move! For example, the average speed of a nitrogen molecule with a mass of 14 u (u - unified diminutive mass unit of measurement) at room temperature is most 670 chiliad/south - two times faster than the speed of sound! Moreover, at college temperatures, gas molecules further accelerate. As a result, they button harder against their surroundings, expanding the volume of the gas (information technology is described past the ideal gas law formula). And the college the book with the same amount of particles, the lower the density. Therefore, air's density decreases every bit the air is heated.

The opposite outcome is achieved with pressure. Imagine that yous have a gas cylinder with a constant volume. The increased pressure level of the cylinder translates into the increased number of molecules inside - the density of air becomes higher.

Altitude has a pregnant influence on air density because every bit yous go higher, the greater the pressure and temperature drops. At high altitudes, the amount of oxygen in the air per unit of measurement volume is lower, because there is less air in full. Therefore, if climbers decide to reach the tops of the highest mountains, they usually need an oxygen cylinder with a mask to be able to exhale. This problem doesn't announced in airplanes since cabins are pressurized to go along the air density inside like to footing level. To get a feeling of how air properties changes with the altitude, take a look at the post-obit air density table for dry out air (data from the NASA Technical Report Server, U.South. Standard Atmosphere, 1976). It follows that the density of dry air at 16 000 ft (~ five km) is nearly two times lower than the density at the sea level.

Altitude [ft (one thousand)]	Temperature [°F (°C)]	Pressure [psi (hPa)]	Air density [lb / cu ft (kg / m³)]
body of water level	59 (fifteen)	14.7 (1013.25)	0.077 (1.23)
two 000 (610)	51.9 (11.1)	13.seven (941.vii)	0.072 (1.xvi)
4 000 (1219)	44.7 (7.ane)	12.7 (873.3)	0.068 (1.09)
6 000 (1829)	37.vi (3.i)	xi.seven (808.ii)	0.064 (1.02)
8 000 (2438)	30.5 (-0.eight)	10.8 (746.2)	0.06 (0.95)
ten 000 (3048)	23.3 (-4.8)	10 (687.3)	0.056 (0.ix)
12 000 (3658)	xvi.two (-8.viii)	ix.two (631.half-dozen)	0.052 (0.84)
14 000 (4267)	nine.1 (-12.8)	8.4 (579)	0.048 (0.77)
16 000 (4877)	1.ix (-sixteen.7)	seven.7 (530.9)	0.045 (0.72)

Density of air in kg / g³ and density of air in English units

The SI unit of measurement for density is kilogram per cubic meter (kg / g³). However, in some cases information technology is more than convenient to apply:

• gram per cubic centimeter (g /c m³), 1 thousand/cm³ = 0.001 kg / m³;
• kilogram per liter (kg / Fifty), 1 kg/L = 1000 kg / thou³;
• gram per milliliter (g / mL), 1 thou/mL = 1000 kg / chiliad³.

The option of units depends on the situation. Sometimes you know the volume of the air container in liters, another time you need to measure its dimensions to obtain book in cubic meters. Feel complimentary to change the units in our air density reckoner!

The same applies to the density of air in Royal units. Case of these units include:

• pound per cubic feet (lb / cu ft);
• pound per cubic thousand (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 / The states gal), one lb / U.s. gal ≈ 7.48 lb / cu ft.

If yous need to catechumen mass density units of any solids, liquids or gases, our density converter may be exactly the tool you were looking for!

In physics, there are also other types of density. Check out the energy density of fields computer and the number density calculator to learn more about them! The main difference is in the units. In the sometime, there are joules instead of kilograms, and in the latter, kilograms are replaced past a dimensionless number.

Standard air density

Because temperature and air pressure vary from identify to identify, we need to define reference air weather condition. Recently, there has been a variety of alternative definitions for the standard conditions (for example in technical or scientific calculations). If you study or piece of work in the technology, applied science or chemical industries, you should always cheque what standards were used by the author of the publication, commodity or volume. You demand to know what they meant by "standard" conditions. Not only do the standards change on a regular basis, but they are also set by diverse organizations (some have even more than one definition of standard reference weather). In the list beneath, you can discover several standard reference pressures p₀ and temperatures T₀ in current apply (recall that there are many more of them):

• International Union of Pure and Applied Chemistry(IUPAC): Standard Temperature and Pressure (STP), p₀ = 10⁵ Pa, T = 0 °C;
• Institute of Standards and Engineering (NIST): ISO 10780, p₀ = 1 atm, T = 0 °C;
• International Civil Aviation System (ICAO): International Standard Temper (ISA), p₀ = 1 atm, T = fifteen °C;
• The states Environmental Protection Agency (EPA): Normal Temperature and Pressure level (NTP), p₀ = 1 atm, T = 20 °C;
• International Union of Pure and Practical Chemistry: Standard Ambient Temperature and Pressure (SATP), p₀ = 10⁵ Pa, T = 25 °C;

So, if you desire to reply the question what is the standard air density, y'all should choose the advisable standard conditions. You can compute them with our air density calculator with an assumption that relative humidity is relatively small-scale (dry out air). For example, the standard air density for STP is ρ₀ = i.2754 kg / grand³, for NIST is ρ₀ = 1.2923 kg / thou³ and for SATP is ρ₀ = 1.1684 kg / m³.

What is air pressure?

Air pressure is a physical property of a gas that tells us with how much strength it has when acting on the surroundings. Let'south consider a cubic container (come across figure below) with some air closed inside. According to the kinetic theory of gases, the molecules of the gas are in constant motion with a velocity that depends on the thermal free energy. Particles collide with each other and with the walls of a container, exerting a tiny strength on them. However, since the number of the enclosed molecules reaches about ~10²³ (gild of magnitude of Avogadro's constant), the total strength becomes significant and measurable - this is pressure level.

There are likewise other types of pressure which we accept described in our other calculators. Now when yous know what is air pressure, you should certainly cheque out hydrostatic pressure computer (force is exerted by liquids) and radiation pressure calculator (strength is exerted by lite) and acquire more than near them!

What is relative humidity?

The relative humidity RH is divers as the ratio of the partial force per unit area of the h2o vapor to the equilibrium vapor pressure level of water at a given temperature. Partial pressure is the pressure level of one component of the air if taken individually, at the same volume and temperature of the whole. When yous sum the partial pressures of all the gases in the air, you will obtain its total pressure which we tin can directly measure:

p_total = p_N₂ + p_O₂ + p_Ar + p_H₂O + ...

The equilibrium vapor pressure of water is the pressure exerted past a vapor that is in thermodynamic equilibrium with its liquid phase at a given temperature. It is a measure out of the tendency of molecules or atoms to escape from a surface of a liquid and become a gas. Equally the temperature increases, the equilibrium vapor force per unit area increases too.

Relative humidity RH ranges between 0% and 100%, where 0% means the dry air, and 100% is air that is completely saturated with water vapor. You should exist enlightened that relative humidity of 100% doesn't mean that air only consists of water. When relative humidity is of 100%, the cooling of the air gives rise to condensation of water vapor.

What is the dew point?

Dew point is a concrete quantity that is strictly related to the humidity of air. It is the temperature at which the water vapor contained in air reaches its saturation state. When the air is further cooled, the water vapor volition condense to grade liquid water - dew. There are several ways to approximate the dew point. Our air density estimator uses the post-obit formula:

DP = 243.12 * α / (17.62 - α),

where α is a parameter that depends on the relative humidity RH and temperature T:

α = ln(RH/100) + 17.62 * T / (243.12 + T).

Relative humidity is expressed in percents and temperature in Celsius degrees. Considering dew indicate is straight linked to relative humidity you need to enter but one of those parameters in the air density estimator.

Human body uses the evaporation of sweat to cool downwards during a hot solar day. The evaporation speed of the perspiration depends on how much moisture is in the air. If the air is already saturated (relative humidity = 100%), perspiration will not evaporate, and you will be coated with sweat. Thankfully, when air is moved from your body by a wind, sweat volition evaporate faster, making you lot feel a pleasant coolness. Discomfort also arises when the dew point is low (dry out air) causing the skin to crack and go irritated more easily.

In the tabular array beneath, yous will find dew signal and (related to information technology) relative humidity at the temperature of 68°F (20°C). The dew point can't exist college than the air temperature because relative humidity can't exceed 100%. On the other paw, when relative humidity equals 0%, we say that the air is a dry air (dew point loses its purpose because there is no water).

Dew point [°F (°C)]	Relative humidity at 61.6°F (20°C) [%]
over 60 (xvi.4)	over fourscore
57.8 (14.3)	lxx
53.6 (12)	threescore
48.vii (9.iii)	50
42.8 (6)	40
35.4 (1.9)	xxx
beneath 25.four (-3.7)	below than 20

Dominik Czernia , PhD candidate and Bogna Szyk

Air pressure at distance Cloud base Density altitude … 8 more

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Source: https://www.omnicalculator.com/physics/air-density

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