—
L
22.4147
L/mol
1.292456
g/L
1.0218
mol
1
atm
273.15
K
—
L
22.4147
L/mol
1.292456
g/L
1.0218
mol
1
atm
273.15
K
The STP Calculator converts gas properties measured at any temperature and pressure to their equivalent values at Standard Temperature and Pressure (STP). STP is defined as 0 °C (273.15 K) and 1 atm (101.325 kPa), serving as a universal reference point for comparing gas quantities across different experimental conditions.
The conversion relies on the combined gas law, derived from the ideal gas law $$PV = nRT$$. By holding the number of moles constant, we can relate initial and final states:
$$\frac{P_1 V_1}{T_1} = \frac{P_2 V_2}{T_2}$$
At STP, one mole of an ideal gas occupies exactly 22.414 L, a cornerstone value in chemistry. This calculator first determines the number of moles from your current conditions, then computes the volume those moles would occupy at STP. This is essential for stoichiometric calculations, gas comparisons, and laboratory work where measurements are taken at ambient conditions but must be reported at STP.
The calculator performs a two-step process. First, it determines the number of moles present using your current conditions:
$$n = \frac{PV}{RT}$$
where R = 0.08206 L·atm/(mol·K). Then it calculates the volume at STP:
$$V_{STP} = \frac{nRT_{STP}}{P_{STP}} = n \times 22.414 \text{ L/mol}$$
The molar volume at STP is a constant for ideal gases: $$V_m = \frac{RT_{STP}}{P_{STP}} = \frac{0.08206 \times 273.15}{1} = 22.414 \text{ L/mol}$$. The density output uses the average molar mass of dry air (28.97 g/mol) as a reference. For a specific gas, multiply the mole count by its molar mass and divide by the STP volume to get the actual density.
Note that IUPAC redefined STP in 1982 to 0 °C and exactly 1 bar (100 kPa), giving a molar volume of 22.711 L. This calculator uses the traditional chemistry definition of 1 atm, which remains widely used in education and engineering.
The volume at STP tells you how much space your gas sample would occupy under standard conditions. A volume larger than your current volume means your gas is currently compressed (high P or low T). A smaller STP volume means your gas is currently expanded (low P or high T). The moles calculated should match your input if conditions are consistent. Use this to verify experimental measurements or convert between mass and volume of gases.
Inputs
Results
At 25°C and 1 atm, 25 L contains ~1.022 mol, which occupies 22.91 L at STP — slightly more than one molar volume.
Inputs
Results
10 L at 5 atm and 350 K contains 1.74 mol. At STP, this would expand to 39.02 L.
The traditional STP is 0 °C (273.15 K) and 1 atm (101.325 kPa). IUPAC redefined STP in 1982 as 0 °C and 1 bar (100 kPa), giving a molar volume of 22.711 L. This calculator uses the traditional 1 atm definition, which is still standard in most chemistry courses.
STP is 0 °C and 1 atm. NTP (Normal Temperature and Pressure) is 20 °C (293.15 K) and 1 atm, giving a molar volume of ~24.04 L. SATP (Standard Ambient) is 25 °C and 1 bar. Always check which standard is required for your application.
It follows directly from the ideal gas law: $$V_m = \frac{RT}{P} = \frac{0.08206 \times 273.15}{1} = 22.414$$ L/mol. This is an exact consequence of the gas constant R and the chosen reference conditions.
The calculator uses the ideal gas law, which works well at moderate conditions. For gases near liquefaction, at very high pressures (>10 atm), or at very low temperatures, real gas corrections (Van der Waals, compressibility factor) should be applied.
Multiply the moles at STP by the molar mass: $$m = n \times M$$. For example, 22.414 L of O₂ at STP = 1 mol × 32 g/mol = 32 g.
Yes, the ideal gas law applies to mixtures. The total volume at STP reflects the total moles of all gas species combined. To find individual gas volumes, use the mole fraction of each component multiplied by the total STP volume.
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