The gas stoichiometry calculator converts between moles, grams, and volume (liters) for ideal gases at standard conditions. Use STP (0°C, 1 atm, 22.4 L/mol) or NTP (25°C, 1 atm, 24.5 L/mol) to interconvert gas quantities in stoichiometry problems.
Gas Quantity Converter
Step-by-Step
How to Use the Gas Stoichiometry Calculator
Gas stoichiometry connects the mass, moles, and volume of gases in chemical reactions. At standard conditions, one mole of any ideal gas occupies a fixed volume — 22.4 L at STP or 24.5 L at NTP.
Step 1: Select the Gas
Choose a common gas from the dropdown or enter a custom molar mass. The molar mass converts between grams and moles.
Step 2: Choose Standard Conditions
STP (0°C, 1 atm) is traditional and used in most textbooks: molar volume = 22.4 L/mol. NTP (25°C, 1 atm) is used in biology and engineering: molar volume = 24.5 L/mol. Use Custom to enter any molar volume from the ideal gas law (PV=nRT).
Step 3: Enter Amount
Enter your known quantity as grams, moles, or liters. The calculator converts to all three representations simultaneously.
Example: CO₂ from Combustion
If you produce 2.5 mol CO₂ from burning propane: grams = 2.5 × 44.01 = 110.03 g. Volume at STP = 2.5 × 22.4 = 56.0 L. Volume at NTP = 2.5 × 24.5 = 61.25 L.
Frequently Asked Questions
What is molar volume at STP?
At STP (Standard Temperature and Pressure: 0°C and 1 atm), one mole of any ideal gas occupies 22.4 liters. At NTP (Normal Temperature and Pressure: 25°C and 1 atm), one mole occupies 24.5 liters. These standard conditions simplify gas stoichiometry calculations.
How do I convert grams of gas to liters?
Step 1: Calculate moles = mass (g) ÷ molar mass (g/mol). Step 2: Multiply moles by 22.4 L/mol (at STP) or 24.5 L/mol (at NTP). For example, 32g of O₂ (molar mass 32 g/mol) = 1 mol = 22.4 L at STP.
What is the difference between STP and NTP?
STP (Standard Temperature and Pressure) is 0°C (273.15 K) and 1 atm — molar volume = 22.4 L/mol. NTP (Normal Temperature and Pressure) is 25°C (298.15 K) and 1 atm — molar volume = 24.5 L/mol. NTP is more common in biological and chemical lab settings.
Is this calculator free?
Yes, completely free with no signup required. All calculations run in your browser.
Does this work for all gases?
Yes, for ideal gases. Most common gases (O₂, N₂, CO₂, H₂, CH₄) behave nearly ideally at standard conditions. For very high pressures or very low temperatures, real gas behavior deviates and the van der Waals equation would be needed.