Last updated: July 3, 2026
STP Calculator (Standard Temperature and Pressure)
Creators
Dharmendra SinghReviewers
Creators
Dharmendra SinghReviewers
Quick Answer
The STP calculator uses 273.15 K and 1 atm, where an ideal gas has molar volume 22.414 L/mol. It converts moles, mass plus molar mass, or measured gas volume at pressure and temperature into volume at STP and moles.
At the common chemistry STP of zero degrees Celsius and one atmosphere, one mole of an ideal gas occupies 22.414 litres. Volume at STP equals moles times 22.414 litres per mole.
Key Takeaways
- This calculator uses the common STP convention of 273.15 K and 1 atm.
- At that STP, one mole of ideal gas occupies 22.414 L.
- Use V_STP = n × 22.414 L/mol to convert moles to litres.
- Use n = V_STP / 22.414 to convert litres at STP to moles.
- For non-STP measurements, use V_STP = V × (P/P_STP) × (T_STP/T).
Creators
Dharmendra SinghReviewers
Creators
Dharmendra SinghReviewers
Formula
V_STP = n × 22.414 L/mol; n = V_STP / 22.414; V_STP = V × (P/P_STP) × (T_STP/T)
Where:
- V_STP=Gas volume at standard temperature and pressure(L)
- n=Amount of gas(mol)
- 22.414=Ideal-gas molar volume at 0 °C and 1 atm(L/mol)
- P_STP=STP pressure used by this calculator(1 atm)
- T_STP=STP temperature(273.15 K)
- V, P, T=Measured gas volume, pressure, and absolute temperature(L, atm, K)
- M=Molar mass for mass-to-moles conversion(g/mol)
Worked Examples
Two moles of gas at STP
Convert a known amount of ideal gas to litres at the 0 °C, 1 atm STP convention.
- 1Use the pre-1982 IUPAC molar volume: 22.414 L/mol at 273.15 K and 1 atm.
- 2Multiply moles by molar volume: V_STP = 2 mol × 22.414 L/mol.
- 3The volume is 44.828 L at STP.
Half a mole from an STP volume
A gas sample already measured at STP occupies 11.207 L.
- 1Use n = V_STP ÷ 22.414 L/mol.
- 2n = 11.207 L ÷ 22.414 L/mol.
- 3The sample contains 0.5 mol of gas.
Oxygen mass to STP volume
Convert 32 g of O2 with molar mass 32 g/mol to ideal-gas volume at STP.
- 1Convert mass to moles: n = 32 g ÷ 32 g/mol = 1 mol.
- 2Use V_STP = n × 22.414 L/mol.
- 3One mole of ideal gas occupies 22.414 L at this STP convention.
Introduction
The STP calculator converts ideal-gas measurements to standard temperature and pressure. This page uses the common teaching convention of 0 °C (273.15 K) and 1 atm, where one mole of an ideal gas occupies 22.414 L. That is the pre-1982 IUPAC STP convention used in many general-chemistry problems. Modern IUPAC standard pressure is 100 kPa, which gives a molar volume near 22.711 L/mol at 273.15 K, so always state which standard you use. For gas identity work, pair this tool with the molar mass of gas calculator and for mixtures use the partial pressure calculator. The assumptions follow ideal-gas relationships and standards documented by IUPAC and NIST.
What does STP mean in chemistry?
STP stands for standard temperature and pressure. It provides a reference state so gas volumes can be compared without ambiguity. This calculator uses 273.15 K and 1 atm as the primary STP definition because it matches the familiar ideal-gas molar volume of 22.414 L/mol.
- Temperature:
0 °C = 273.15 K.
- Pressure:
1 atm in this calculator.
- Ideal-gas molar volume:
22.414 L/mol.
Modern IUPAC standard pressure is 100 kPa, giving about 22.711 L/mol at 273.15 K.
STP molar volume formula
For an ideal gas at 0 °C and 1 atm, volume is directly proportional to moles. Use V_STP = n × 22.414 L/mol when you know moles. Use n = V_STP / 22.414 when you know the STP volume. If moles come from a mass, first calculate n = mass / molar mass, the same bridge used in stoichiometry and the molarity calculator for solution work.
The 22.414 L/mol shortcut applies to ideal gases at the stated STP only; it is not a liquid or solid molar volume.
Converting measured volume to STP
When a gas is measured away from STP, convert it using the combined gas law: V_STP = V × (P/P_STP) × (T_STP/T). Pressure and temperature must be absolute units: atm for pressure in this calculator and kelvin for temperature. The pressure factor compresses or expands volume, while the temperature factor corrects thermal expansion.
Record V in litres.
Convert pressure to atm.
Convert temperature to kelvin.
Multiply by P/1 atm and by 273.15/T.
Worked verification examples
The calculator is designed around transparent textbook checks. Two moles give 2 × 22.414 = 44.828 L at STP. A volume of 11.207 L at STP gives 0.5 mol. A 32 g oxygen sample with M = 32 g/mol is 1 mol and therefore 22.414 L. A 10 L gas at 2 atm and 546.3 K converts to 10 L at STP because the doubled pressure and doubled absolute temperature cancel.
1 atm STP versus 100 kPa STP
The phrase STP is not universal unless the definition is stated. Many school problems use 1 atm and 273.15 K. IUPAC later recommended 100 kPa as standard pressure, still at 273.15 K for STP discussions, which changes the ideal-gas molar volume to about 22.711 L/mol. For high-precision work, report the exact P and T instead of only saying STP.
| Convention | Temperature | Pressure | Ideal molar volume |
|---|---|---|---|
| Common/pre-1982 STP | 273.15 K | 1 atm | 22.414 L/mol |
| Modern IUPAC standard pressure | 273.15 K | 100 kPa | ≈22.711 L/mol |
| SATP example | 298.15 K | 100 kPa | ≈24.789 L/mol |
Practical tips and common mistakes
Most STP mistakes come from mixing pressure units, using Celsius directly in gas-law equations, or applying the 22.414 L/mol shortcut away from STP. Convert °C to K before calculating and keep the pressure standard consistent with the molar volume. For broader context on ideal gases, see LibreTexts gas laws and the OpenStax chemistry gas chapter.
If pressure and temperature are entered with volume, this calculator treats the volume as a measured non-STP volume and converts it to STP.
Quick Reference Card
STP Gas Calculations — Quick Reference
Quick reference • STP Calculator (Standard Temperature and Pressure)
V_STP = n×22.414; n = V_STP/22.414; V_STP = V×(P/1 atm)×(273.15/T)Valid range: Positive finite values for ideal gases; pressure in atm, volume in L, temperature in K
Common Values
⚠ Watch Out
- •Do not use Celsius directly in the combined gas law; convert to kelvin.
- •Do not mix 1 atm and 100 kPa STP conventions without stating the standard.
- •Use 22.414 L/mol only for ideal gases at 0 °C and 1 atm.
- •Real gases can deviate from the ideal molar volume near condensation or high pressure.
Pro Tips
- →Keep extra digits during calculation, then round the final STP volume.
- →If a problem says STP in general chemistry, check whether it expects 1 atm or 100 kPa.
- →When pressure is given in kPa, divide by 101.325 to convert to atm for this calculator.
- →Use mass divided by molar mass first when converting grams of a gas to STP volume.
FAQs
What molar volume does this STP calculator use?
It uses 22.414 L/mol, corresponding to an ideal gas at 0 °C (273.15 K) and 1 atm. That is the common pre-1982 IUPAC and teaching convention.
How do I calculate gas volume at STP from moles?
Multiply moles by 22.414 L/mol. For example, 2 mol of ideal gas occupies 44.828 L at 0 °C and 1 atm.
How do I calculate moles from a gas volume at STP?
Divide the STP volume in litres by 22.414 L/mol. For example, 11.207 L at STP corresponds to 0.5 mol.
How do I convert a measured gas volume to STP?
Use V_STP = V × (P/1 atm) × (273.15 K/T). Enter pressure in atm and temperature in kelvin so the ratios are dimensionally consistent.
Why is modern IUPAC STP sometimes 22.711 L/mol?
Modern IUPAC standard pressure is 100 kPa rather than exactly 1 atm. At 273.15 K, an ideal gas at 100 kPa has a larger molar volume, about 22.711 L/mol.
Can I use STP molar volume for real gases?
It is an ideal-gas approximation. Many gases are close at low pressure, but real gases deviate because molecules have volume and intermolecular forces.