Absolute Humidity Calculator — g/m³ from Temperature & RH
Enter air temperature and relative humidity to get the water-vapour mass per cubic metre, the dew point, and the saturation vapour pressure using the Magnus formula.
°C
%
Mass of water vapour per cubic metre of air
- 1
Saturation vapour pressure
6.112 × exp(17.67 × 20 ÷ (20 + 243.5)) = 23.369 hPaMagnus formula: maximum water vapour pressure the air can hold at this temperature. - 2
Actual vapour pressure
(60 ÷ 100) × 23.369 = 14.0217 hPa - 3
Absolute humidity
216.7 × 14.0217 ÷ 293.15 = 10.365
How does this calculator work?
Absolute humidity (g/m³) = 216.7 × (RH/100 × e_s) / T_kelvin, where e_s (hPa) comes from the Magnus formula. Enter temperature and relative humidity to get the water-vapour density, dew point, and how close the air is to saturation.
Formula
How this is calculated
Relative humidity tells you how full the air is as a fraction of its maximum holding capacity, but the actual water-vapour mass depends on temperature too — warm air can hold far more. Absolute humidity (AH, g/m³) gives the true vapour-mass density regardless of temperature.
The calculation uses two steps. First, the Magnus formula estimates the saturation vapour pressure e_s = 6.112 × exp(17.67 × T / (T + 243.5)) in hPa, the pressure at which air of temperature T is fully saturated. Multiplying by RH/100 gives the actual vapour pressure e_a. Second, the ideal-gas law for water vapour converts that pressure to mass density: AH = (M_w / R) × e_a / T_K = 216.7 × e_a / T_K, where T_K is temperature in kelvin and 216.7 ≈ 18.015 g/mol ÷ 0.08314 hPa·m³/(mol·K).
The dew point is back-solved from e_a using the same Magnus equation. This calculator is valid for −40 to 60 °C; the Magnus formula loses accuracy beyond that range. It also assumes standard sea-level atmospheric pressure (~1013 hPa); at high altitude the results differ slightly.
Frequently asked questions
Relative humidity (%) is the ratio of actual to saturation vapour pressure — how "full" the air is as a fraction of its capacity. Absolute humidity (g/m³) is the actual mass of water vapour per cubic metre of air, independent of the temperature-dependent capacity.
Two rooms at the same relative humidity but different temperatures hold very different amounts of moisture. HVAC engineers, conservators, and physiologists use absolute humidity to size dehumidifiers, protect materials, and assess respiratory load, because AH directly measures actual moisture present.
The dew point is the temperature at which the current air mass would reach 100% RH and condensation would start. It is computed by inverting the Magnus formula for the actual vapour pressure e_a. The closer the dew point is to air temperature, the more humid conditions feel.
TG we-Calculate Editorial Team. (2026). Absolute Humidity Calculator — g/m³ from Temperature & RH [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/absolute-humidity-calculator
TG we-Calculate Editorial Team. "Absolute Humidity Calculator — g/m³ from Temperature & RH." TG we-Calculate. 2026. https://we-calculate.com/calculator/absolute-humidity-calculator.
TG we-Calculate Editorial Team, "Absolute Humidity Calculator — g/m³ from Temperature & RH," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/absolute-humidity-calculator
@misc{wecalculate_absolute_humidity_calculator, title = {Absolute Humidity Calculator — g/m³ from Temperature & RH}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/absolute-humidity-calculator}}, year = {2026}, note = {TG we-Calculate} }
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