🔲 Reference States
old and new standards
Current STP (IUPAC - Modern)
STPThe current scientific standard since 1982. Defined as 273.15 K (0 °C) and an absolute pressure of exactly 100 kPa (1 bar). The molar volume of an ideal gas is 22.71 L/mol.
Old STP (Pre-1982 / NIST)
STP (old)The classic standard of 0 °C and 1 atm (101.325 kPa). Many legacy textbooks and US-based sensors still use this as the reference for 'Standard' conditions.
NTP (ISO / DIN)
NTP / Nm³Normal Temperature and Pressure. This is the basis for the 'Normal Cubic Meter' (Nm³). Defined at 273.15 K (0 °C) and 101.325 kPa (1 atm). Note: In HVAC engineering, 20 °C is sometimes used as 'Normal'.
SATP (Thermodynamics)
SATPStandard Ambient Temperature and Pressure. Used for thermodynamic tables (ΔH°, ΔG°). It assumes 298.15 K (25 °C) and 1 bar. Molar volume: 24.79 L/mol.
Quick Reference: Ideal Gas Molar Volume ($V_m$)
| Standard | Temp. | Pressure | Molar Volume ($V_m$) |
|---|---|---|---|
| STP (Modern) | 0 °C | 100 kPa | 22.71 L |
| STP (Old) | 0 °C | 101.325 kPa | 22.41 L |
| NTP | 0 °C | 101.325 kPa | 22.41 L |
| SATP | 25 °C | 100 kPa | 24.79 L |
| SCTP | 15.56 °C | 101.325 kPa | 23.68 L |
Attention: In chemistry, always use the 100 kPa (1 bar) standard for modern calculations, unless explicitly stated that the old 1 atm standard is used.