A calculation device includes: an acquisition unit that obtains a mass concentration of particles in a gas measured in a first measurement station, a number concentration of particles in the gas measured in a second measurement station, and a humidity of the gas measured in the second measurement station; and a calculation unit that calculates a function, which defines a relationship of a mass concentration and a number concentration to a humidity and is used to calculate a mass concentration of particles in the gas in a third measurement station from a number concentration of particles in the gas and a humidity of the gas measured in the third measurement station, based on the mass concentration in the first measurement station and the number concentration and the humidity in the second measurement station, the third measurement station being installed in a different location from the first and second measurement stations.