Dalton's law describes how a gas's percentage affects its contribution to total pressure.

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Dalton's law says the total pressure of a gas mixture is the sum of the partial pressures of its components. Each gas contributes a partial pressure equal to its mole fraction (its percentage in the mixture) times the total pressure: P_total = P1 + P2 + P3 ... and Pi = Xi × P_total. So a gas that makes up a larger portion of the mixture contributes more to the total pressure, but the overall pressure is still the sum of all partial pressures, not a product. The molecular weight of a gas or which gas is heavier doesn’t set the total pressure by itself; it’s the amount (moles) of each gas at the given temperature and volume that matters.