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Calculation Machine

Air Density Calculator

Air density from temperature, pressure and altitude.

Reviewed by James Whitfield · How we check our maths

Your values

ⓘ Live results

Results
Air density
1.2041 kg/m³
In lb/ft³
0.07517
Barometric pressure
101.33 kPa
Density ratio vs sea level 20°C
1

Quick answer

Air density falls as temperature rises and as altitude increases, which reduces the mass of air a fan delivers.

The formula

rho = P / (R x T)

Worked example

Worked example

Using the values the calculator loads with.

Inputs

  • Air temperature20 °C
  • Altitude0 m

Result

  • Air density1.2041 kg/m³
  • In lb/ft³0.07517
  • Barometric pressure101.33 kPa
  • Density ratio vs sea level 20°C1

How to use the Air Density Calculator

  1. 1Enter the air temperature and site altitude.
  2. 2Read density and the ratio against standard conditions.
  3. 3Divide standard CFM by the density ratio to size fans at altitude.

Frequently asked questions

Why does altitude matter for HVAC?

Thinner air carries less heat, so you need more CFM for the same capacity above about 750 m.

Does humidity change it?

Slightly — moist air is a little lighter than dry air at the same temperature.

About this calculator