Flow rate calculation system and flow rate calculation method

To accurately calibrate fluid control equipment. A flow rate calculation system includes: a container in which gas is enclosed; a weight measurement part on which the container is disposed; a gas line which connects the container and fluid control equipment and in which the gas flows; and an enclosing line for enclosing the gas in the container disposed on the weight measurement part, thereby allowing the gas to flow from the container to the fluid control equipment or from the fluid control equipment to the container in a state that the container is disposed on the weighing measurement part, and calculating a flow rate of the gas flowing to the fluid control equipment based on an output value outputted from the weight measurement part, and the container and the weight measurement part are adapted to be placed in a decompressed decompression chamber.