Gas Density from Molar Mass

\rho = \frac{PM}{RT}

ρ =

P =

M =

T =

Enter your known values, leave one input blank, and solves for the missing one. Try different units for next level excitement!

Constant used — built into this formula, no need to enter

R = 8.31446261815324\ \text{J/(mol}{\cdot}\text{K)}

Molar gas constant · exact

Learning zone

Substituting m = nM into the ideal gas law shows that a gas's density is fixed by three things: molar mass, pressure, and absolute temperature, tied together by R = 8.314462618 J/(mol·K). At room conditions air (M ≈ 29 g/mol) comes out near 1.2 kg/m³ while helium (4 g/mol) is about 0.17 kg/m³ — the whole physics of party balloons in one ratio. The molar-mass rearrangement is a classic lab method for identifying an unknown vapor.

Gas Density from Molar Mass

\rho = \frac{PM}{RT}

Where

$\rho$ = Gas density
$P$ = Pressure
$M$ = Molar mass
$T$ = Absolute temperature

Missing one of these? Work it out first, then come back

Gas density — Density, Fourier Number
Pressure — Ideal Gas Law, Partial Pressure from Mole Fraction
Molar mass — Moles from Mass (n = m/M), Equivalent Weight from Molar Mass and Valence
Absolute temperature — Osmotic Pressure (Π = MRT), Kp from Kc (Kp = Kc(RT)^Δn)