Chemistry

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Standard Temperature and Pressure Calculator.

Compare the declared IUPAC 100 kPa and legacy 1 atm STP conventions without silently choosing one.

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Set your values

Results update as you type.

Pressure: 100 kPa

Pressure

100.000000kPa
Temperature: 273.15 K

Temperature

273.150000K
Molar volume: 22.710955 L

Molar volume

22.710955L
Sample volume: 22.710955 L

Sample volume

22.710955L

How to Use

Every model convention and source-dependent parameter is visible. Results update automatically after each edit.

Use Cases

Compare STP conventions for chemistry problems

Quickly see the difference between IUPAC and legacy STP values to ensure you use the correct one in your calculations.

Example: When calculating molar volume, use 22.7 L/mol for IUPAC STP and 22.4 L/mol for legacy STP.

Reference for educational purposes

Use the calculator as a quick reference to understand how the two STP definitions differ and when each is applied.

Example: In a classroom, compare the pressure values to explain why IUPAC updated the standard.

Frequently Asked Questions

What is the difference between IUPAC STP and legacy STP?
IUPAC STP is defined as 0°C (273.15 K) and 100 kPa (1 bar), while legacy STP is 0°C and 1 atm (101.325 kPa). The calculator lets you compare these two conventions without choosing one.
Why does the calculator not ask for temperature or pressure inputs?
The calculator is designed to compare the two standard conventions directly. It uses the fixed values for each convention: 0°C for temperature, and 100 kPa or 1 atm for pressure, so no additional inputs are needed.
Can I use this calculator for gas law calculations?
Yes, you can use the standard temperature and pressure values provided by the calculator as reference conditions for gas law calculations, such as molar volume. However, always ensure you are using the correct convention for your specific application.

Tips & Common Mistakes

Tips

  • Always check which STP convention your textbook or exam uses before applying values.
  • Remember that IUPAC STP uses 100 kPa, while legacy STP uses 1 atm (101.325 kPa).
  • Use the calculator to see the numerical difference in pressure and understand its impact on gas volume calculations.
  • For precise scientific work, follow the convention specified by your institution or publication.

Common Mistakes to Avoid

  • Assuming that STP always means 1 atm; IUPAC now defines it as 100 kPa.
  • Using the wrong molar volume (22.4 L vs 22.7 L) because you mixed up the conventions.
  • Forgetting that temperature is the same (0°C) in both conventions, so the difference is only in pressure.

Last updated: August 13, 2026