Oxygen & Gas Composition Calculators

Combustion Gas Composition Calculator

Calculate the nitrogen percentage of combustion gas by difference from measured CO2%, O2%, and CO% using the Orsat analysis approach.

Exhaust Gas Composition Calculator

Calculate the mass-percentage composition of exhaust gas from the masses of CO2, H2O, N2, and O2 present.

Gas Density Calculator

Calculate gas density from pressure, molar mass, and temperature using the ideal gas law.

Gas Expansion Calculator

Calculate the new volume of a fixed quantity of gas after a change in pressure and temperature using the combined gas law.

Gas Mixing Calculator

Calculate the flow-weighted average concentration when two gas streams with different flow rates and compositions are mixed together.

Ideal Gas Combustion Calculator

Calculate the volume occupied by combustion product gases using the ideal gas law from moles, temperature, and pressure.

Oxygen Concentration Calculator

Calculate the volumetric oxygen concentration of a gas stream from oxygen flow and total gas flow.

Oxygen Requirement Calculator

Calculate the theoretical mass of pure oxygen needed to completely combust one kilogram of fuel from its ultimate analysis.

Tracking Exactly What's in the Gas Mixture

Combustion involves several overlapping gas composition questions — how much oxygen a reaction actually needs, what the resulting exhaust gas mixture looks like, and how gases behave when mixed or expanded. Eight calculators here apply gas law and combustion chemistry fundamentals to these composition questions.

Popular Oxygen & Gas Composition Calculators

Eight tools span oxygen demand and gas mixture behavior:

  • Oxygen Requirement Calculator — calculates the oxygen needed for complete combustion of a given fuel quantity.
  • Combustion Gas Composition Calculator — calculates the full product gas composition from a combustion reaction.
  • Gas Density Calculator — calculates gas density from molecular weight, temperature, and pressure using the ideal gas law.
  • Gas Mixing Calculator — calculates the resulting composition when two or more gas streams are combined.
  • Ideal Gas Combustion Calculator — applies the ideal gas law to combustion gas volume and pressure relationships.

Why Gas Density Changes So Much With Temperature

Combustion gases behave close enough to an ideal gas that density scales inversely with absolute temperature at constant pressure — which is exactly why hot flue gas is so much less dense than the surrounding cool air, the density difference that drives natural stack draft in the first place. This same relationship is why gas volume flow calculations always need to specify a temperature and pressure basis (standard conditions versus actual operating conditions), since the same mass of gas occupies very different volumes depending on how hot and how pressurized it is.

Frequently Asked Questions

Why does oxygen requirement depend on more than just fuel quantity?
Fuel composition (carbon, hydrogen, sulfur content) determines the actual stoichiometric oxygen demand per unit of fuel, so two fuels of the same mass can require meaningfully different oxygen quantities for complete combustion.

Explore More

Need the air-side stoichiometry behind these numbers? See the Air & Fuel Calculators, or check flue gas composition specifically in the Flue Gas Calculators.