A flow measurement apparatus can include a main flow passage, a variable flow restrictor, a bypass flow passage having an inlet connected with the main flow passage upstream of the variable flow restrictor and an outlet connected with the main flow passage downstream of the variable flow restrictor, and a mass flowmeter connected in the bypass flow passage between the inlet and the outlet. A method can include connecting a flow measurement apparatus, so that a fluid flow in a well also flows through the flow measurement apparatus, and varying a restriction to the fluid flow through the variable flow restrictor in response to a change in a flow rate of the fluid flow.