Use Dalton’s law: partial pressure = mole fraction × total pressure
Find the mole fraction of the gas: moles of gas ÷ total moles of all gases
Multiply the mole fraction by the total pressure
Use the formula: Pgas = Xgas × Ptotal
If moles and volume are known, use the ideal gas law: P = nRT ÷ V
If a gas is collected over water, subtract water vapor pressure from total pressure: Pgas = Ptotal − Pwater
Keep units consistent when calculating pressure
Convert the final answer to the required pressure unit