STP Gas Law Calculator

Compute any property of an ideal gas using PV = nRT. Supports real‑time unit conversion, predefined gases, and interactive isotherms.

Select unknown variable – the calculator will compute it from the other three.

Calculate:
Gas presets (1g at STP):
O₂ (32 g/mol)
N₂ (28 g/mol)
CO₂ (44 g/mol)
He (4 g/mol)
Sets P=1 atm, T=273.15 K, n = 1g / molar mass
Gas Law Calculation Valid
1. Converted inputs (base units)
P (atm) V (L) n (mol) T (K)
1.000 22.400 1.000 273.150
2. Substitution (R = 0.082057)
PV = nRT → (1.000)(22.400) = (1.000)(0.082057)(273.150)
3. Computed target variable
P = 1.000 atm
Molar volume at STP: 22.414 L/mol

Understanding STP & Ideal Gas Law

Standard Temperature and Pressure (STP) is defined as 0°C (273.15 K) and 1 atm (101.325 kPa). At STP, one mole of an ideal gas occupies 22.414 L (molar volume).

Enhanced features: Real-time validation prevents zero/negative inputs, gas presets now set full STP conditions, and empty fields are gracefully handled.

Applications

  • Gas stoichiometry at standard conditions.
  • Determining molar mass from gas density.
  • Converting between gas amounts and volumes.

Understanding STP & Ideal Gas Law

Standard Temperature and Pressure (STP) is a reference point used for comparing gas properties. Traditional STP is 0 °C (273.15 K) and 1 atm (101.325 kPa). At STP, one mole of an ideal gas occupies 22.414 L.

Ideal Gas Law: PV = nRT

  • P = absolute pressure (atm, Pa, …)
  • V = volume (L, m³, …)
  • n = amount of substance (mol)
  • R = ideal gas constant (0.082057 L·atm/(mol·K))
  • T = absolute temperature (K)

Derived Quantities

  • Molar volume V/n = RT/P (at STP ≈ 22.414 L/mol)
  • Density ρ = (PM)/(RT) where M = molar mass (g/mol)
  • Mass = n × M

Interactive Features

1
Choose a gas preset – automatically sets molar mass.
2
Enter any three values among P, V, T, n (or mass). The fourth is calculated instantly.
3
Watch the isotherm update – the red dot marks your current (V,P) combination.

Frequently Asked Questions

STP (old IUPAC) = 0°C & 1 atm. SATP (standard ambient temperature and pressure) = 25°C & 1 atm. Molar volume at SATP ≈ 24.466 L/mol.

R depends on units. Here we use 0.082057 L·atm/(mol·K). For SI (Pa·m³), R = 8.3145 J/(mol·K).

The calculator assumes ideal behavior. For real gases at high pressure or low temperature, results are approximate.