acalculator

What is the air density?

Type the air temperature and pressure, and the relative humidity or dew point. The air density calculator gives the density of the moist air in kg/m³ and lb/ft³, the dry-air density for comparison, and the vapour pressure.

Your numbers

Units
Humidity
Air density (kg/m³)
1.2211

The air density is 1.2211 kg/m³ (0.07623 lb/ft³).

Air density (lb/ft³)
0.07623
Of standard sea-level air (%)
99.7
Dry air at the same T and p (kg/m³)
1.225
Vapour pressure (hPa)
8.53
Dry-air pressure (hPa)
1,004.72
Saturation vapour pressure (hPa)
17.05

Air density (kg/m³): 1.2211. The air density is 1.2211 kg/m³ (0.07623 lb/ft³).

How to calculate

Air density calculator: the density of dry or humid air from the temperature, the air pressure and the relative humidity or dew point, in kg/m³ and lb/ft³, with the vapour and dry-air pressures.

Example with the default inputs (Air temperature 58.9999999999999 °F, Air pressure 29.9212555797485 inHg, Humidity Relative humidity, Relative humidity 50%): The air density is 1.2211 kg/m³ (0.07623 lb/ft³).

Method: p_sat(t) = 610.78 × exp(17.27 t ÷ (t + 237.3)) Pa (t in °C); p_v = RH × p_sat(T), or p_sat(dew point), or 0; p_d = p − p_v; ρ = p_d ÷ (287.058 × T) + p_v ÷ (461.495 × T), T in kelvins.

  • Moist air is a mix of ideal gases: dry air and water vapour.
  • The pressure is the actual air pressure where the air is, not an altimeter setting reduced to sea level.

Machine-readable copies: Markdown, JSON.

Worked examples

Each example is checked against the calculator on every build.

  1. Air temperature 59 °F, Air pressure 29.92 inHg, Humidity Dry air gives Air density (kg/m³) 1.224978.Source: Wikipedia, Density of air (ρ = p_d ÷ (R_d T) + p_v ÷ (R_v T); R_d = 287.058, R_v = 461.495 J/(kg·K); Tetens p_sat = 0.61078 exp(17.27 (T − 273.15) ÷ (T − 35.85)) kPa), https://en.wikipedia.org/wiki/Density_of_air (retrieved 2026-10-05)
  2. Air temperature 86 °F, Air pressure 29.92 inHg, Humidity Relative humidity, Relative humidity 100% gives Saturation vapour pressure (hPa) 42.429261, Air density (kg/m³) 1.145936.Source: Wikipedia, Density of air (ρ = p_d ÷ (R_d T) + p_v ÷ (R_v T); R_d = 287.058, R_v = 461.495 J/(kg·K); Tetens p_sat = 0.61078 exp(17.27 (T − 273.15) ÷ (T − 35.85)) kPa), https://en.wikipedia.org/wiki/Density_of_air (retrieved 2026-10-05)
  3. Air temperature 68 °F, Air pressure 26.58 inHg, Humidity Dew point, Dew point 50 °F gives Vapour pressure (hPa) 12.279224, Air density (kg/m³) 1.06399.Source: Wikipedia, Density of air (ρ = p_d ÷ (R_d T) + p_v ÷ (R_v T); R_d = 287.058, R_v = 461.495 J/(kg·K); Tetens p_sat = 0.61078 exp(17.27 (T − 273.15) ÷ (T − 35.85)) kPa), https://en.wikipedia.org/wiki/Density_of_air (retrieved 2026-10-05)

How it works

  • Saturation vapour pressure (Tetens) p_sat(t) = 610.78 × exp(17.27 × t ÷ (t + 237.3)) Pa, with t in °C.
  • Vapour pressure p_v = RH ÷ 100 × p_sat(air temperature), or p_sat(dew point), or 0 for dry air.
  • Dry-air pressure p_d = p − p_v.
  • Air density ρ = p_d ÷ (287.058 × T) + p_v ÷ (461.495 × T), with T in kelvins and pressures in pascals.
  • Dry air at the same T and p = p ÷ (287.058 × T).
  • Of standard sea-level air = ρ ÷ 1.225 × 100%.
  • lb/ft³ = ρ ÷ 16.018463373960138 (1 lb ÷ 1 ft³).

Rules

  • Temperature and dew point from −80 °C to 100 °C; pressure from 10 hPa to 2,000 hPa; relative humidity from 0% to 100%.
  • A dew point above the air temperature, or a vapour pressure at or above the air pressure, has no answer.

Output format

Density in kg/m³ to 4 decimals and lb/ft³ to 5 decimals; the percentage to 1 decimal; pressures in hPa to 2 decimals. All arithmetic is in floats (the exponential).

Worked examples by hand

Standard dry air. 15 °C (288.15 K), 101,325 Pa: ρ = 101,325 ÷ (287.058 × 288.15) = 1.22498 kg/m³.

Saturated warm air. 30 °C, 101,325 Pa, 100% RH: p_sat = 610.78 × exp(17.27 × 30 ÷ 267.3) = 4,242.93 Pa; p_d = 97,082.07 Pa; ρ = 97,082.07 ÷ (287.058 × 303.15) + 4,242.93 ÷ (461.495 × 303.15) = 1.11561 + 0.03033 = 1.14594 kg/m³.

At altitude with a dew point. 20 °C, 90,000 Pa, dew point 10 °C: p_v = 610.78 × exp(172.7 ÷ 247.3) = 1,227.92 Pa; ρ = 88,772.08 ÷ (287.058 × 293.15) + 1,227.92 ÷ (461.495 × 293.15) = 1.06399 kg/m³.

Other questions people ask

How do you calculate air density?

For dry air, ρ = p ÷ (R_d × T) with R_d = 287.058 J/(kg·K) and T in kelvins. At 1,013.25 hPa and 15 °C: 101,325 ÷ (287.058 × 288.15) = 1.225 kg/m³. For humid air, split the pressure into dry air and water vapour and add the two densities.

What is the density of air at sea level?

The standard value is 1.225 kg/m³ (0.0765 lb/ft³), for dry air at 15 °C and 1,013.25 hPa.

Does humidity make air lighter?

Yes. A water molecule (18 g/mol) is lighter than the average air molecule (about 29 g/mol), so at the same temperature and pressure humid air is less dense. Saturated air at 30 °C is about 1.146 kg/m³, against 1.164 kg/m³ dry.

How does temperature change air density?

At a fixed pressure, density is inversely proportional to the absolute temperature: warming air from 0 °C (273 K) to 30 °C (303 K) lowers its density by about 10%.

Should I use the altimeter setting as the pressure?

No. The altimeter setting is reduced to sea level. Use the actual station pressure where the air is; at altitude it is much lower.

What saturation vapour pressure formula is used?

The Tetens formula: 6.1078 × exp(17.27 t ÷ (t + 237.3)) hPa, with t in °C. Wikipedia gives the same formula with T in kelvins.