STP Calculator
Calculate the volume of any ideal gas at standard temperature and pressure (STP) from the number of moles. Furthermore, both IUPAC STP (0°C, 100 kPa, molar volume = 22.711 L/mol) and the older NIST STP (0°C, 1 atm = 101.325 kPa, molar volume = 22.414 L/mol) are supported.
How to use the STP Calculator
Type the amount in moles. Furthermore, for mass: first divide by molar mass to get moles.
IUPAC 2014: 0°C, 100 kPa → 22.711 L/mol. Furthermore, older textbooks use NIST STP (0°C, 1 atm, 22.414 L/mol). Check which standard your course uses.
For mass and density calculations. Furthermore, common values: O₂=32, CO₂=44, CH₄=16, N₂=28, He=4, Cl₂=71.
Volume, mass, and density appear. Moreover, density = M/V_molar at STP — lighter gases have lower density.
Gas volumes at STP are often used in stoichiometry: 1 mol gas = 22.414 L (NIST) allows direct mole-volume conversion. Furthermore, this avoids using PV=nRT for STP-only problems.
Variants, options and when to use each
| Gas | M (g/mol) | Density at NIST STP |
|---|---|---|
| Hydrogen H₂ | 2 | 0.0893 g/L |
| Methane CH₄ | 16 | 0.714 g/L |
| Air (avg) | 29 | 1.293 g/L |
| CO₂ | 44 | 1.964 g/L |
| Chlorine Cl₂ | 71 | 3.164 g/L |
The formula explained
n = moles of gas
V_molar = molar volume at STP (22.414 or 22.711 L/mol)
ρ = gas density at STP (g/L)
At standard temperature and pressure, all ideal gases have the same molar volume — derived from PV = nRT: V_molar = RT/P. Furthermore, IUPAC 2014 STP: T = 273.15 K, P = 100 kPa → V_molar = 22.711 L/mol. Old STP: T = 273.15 K, P = 101.325 kPa → V_molar = 22.414 L/mol. Moreover, 1 mol of any ideal gas occupies this volume regardless of molecular identity.
Worked example — volume of 2.5 mol CO₂ at NIST STP
| Step | Calculation | Result |
|---|---|---|
| V = n × 22.414 | 2.5 × 22.414 | 56.035 L |
| Mass = n × M | 2.5 × 44 | 110.0 g CO₂ |
| Density | 44/22.414 | 1.964 g/L |
What is STP in chemistry?
STP (Standard Temperature and Pressure) defines a reference state for gas calculations. Furthermore, IUPAC (2014 definition): 0°C (273.15 K) and 100 kPa — molar volume = 22.711 L/mol. Older NIST/textbook STP: 0°C and 1 atm (101.325 kPa) — molar volume = 22.414 L/mol. The distinction matters for precise calculations. Moreover, many textbooks still use the old 22.4 L/mol value.STP is distinct from SATP (Standard Ambient Temperature and Pressure): 25°C and 100 kPa — molar volume ≈ 24.789 L/mol. Additionally, NTP (Normal Temperature and Pressure): 20°C and 1 atm — molar volume ≈ 24.055 L/mol. The specific standard used should always be stated in calculations.
Avogadro's law states that at constant T and P, equal volumes of ideal gases contain equal numbers of molecules. Moreover, this is why molar volume is the same for all ideal gases at STP — it depends only on T and P, not on molecular identity.
Who uses this calculator?
Chemistry students use STP molar volume in stoichiometry calculations involving gas volumes. Furthermore, laboratory chemists convert measured gas volumes to moles using the molar volume. Industrial gas companies specify cylinder contents in standard cubic metres (Sm³) at STP conditions. Moreover, environmental scientists report air pollutant concentrations at STP for comparability across different measurement altitudes.
Historical context and related concepts
Gay-Lussac established the law of combining volumes (1808) — equal volumes of gases at the same T and P contain the same number of particles. Furthermore, Avogadro formalised this as Avogadro's law (1811). The IUPAC revision of STP from 1 atm to 100 kPa was made in 1982 and updated in 2014 to align with SI units. Moreover, many textbooks still use the pre-1982 value of 22.414 L/mol — awareness of both values is important.
Why STP calculations are used in stoichiometry, gas analysis, and industrial gas supply
Gas stoichiometry uses STP molar volume to convert between moles and volumes without solving the full ideal gas law. Furthermore, industrial gas specifications (cylinder purity certificates, flow rates) are given at standard conditions (STP or NTP). Moreover, environmental monitoring equipment measures pollutant concentrations — results are normalised to STP to remove the effect of altitude, temperature, and pressure variations.STP in respiratory physiology and clinical spirometry
Lung function measurements (spirometry: FEV₁, FVC) are reported at body temperature and pressure, saturated with water vapour (BTPS: 37°C, 1 atm, 100% RH). Furthermore, converting BTPS to STPD (standard temperature and pressure, dry: 0°C, 1 atm) allows comparison across patients, centres, and time. Moreover, the BTPS to STPD conversion uses combined gas law — a molar volume of ~22.4 L/mol applies only after the STPD correction.
Frequently asked questions
Related tools
Ideal Gas Law Calculator
PV=nRT for non-standard conditions. Furthermore, STP is PV=nRT at T=273.15K and specified P.
→Combined Gas Law Calculator
Convert between any two sets of P,V,T conditions. Moreover, converting to STP uses combined gas law.
→Molar Mass Calculator
Find M for density and mass calculations. Moreover, density at STP = M/22.414 g/L.
→Significant Figures Calculator
Round gas volumes appropriately. Furthermore, molar volume is known to 6 significant figures.
→Charles' Law Calculator
V ∝ T at constant P. Furthermore, STP uses Charles' law to define the standard volume at 273.15 K.
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