System for measuring flow rates of fluid flows to parallel reactors, Which system comprises: - a plurality of reactors, each of the reactors having a reactor inlet, - a common feed line, the common feed line having a common feed line inlet for receiving a fluid from a fluid source and at least one common feed line outlet, the received fluid forming a combined feed flow, the common feed line being adapted to transport said combined feed flow from the common feed line inlet to the common feed line outlet of outlets, - a plurality of reactor feed lines for receiving a reactor fluid flow, which reactor fluid flow is a part of the combined feed flow from the common feed line, and for transporting said reactor fluid flow to at least one of the plurality of reactors, each reactor feed line extending between a common feed line outlet and the reactor inlet of said reactor, - a measurement line, which measurement line has a plurality of measurement line outlets, each of the measurement line outlets connected to one of the reactor feed lines or to one of the reactors, and which measurement line has either one measurement line inlet that is connected to the common feed line or a plurality of measurement line inlets, each of those measurement line inlets being connected to one of the reactor feed lines, - in the measurement line, a first flow sensor for measuring the flow rate of the fluid flow through the measurement line, and - a valve system, comprising one or more valves and a valve control unit for controlling the one or more valves, the valve system being arranged and/or adapted such that it can assume a measurement setting in which the valves redirect one of the reactor feed flows such that it flows through the measurement line. - a plurality of reactors, each of the reactors having a reactor inlet, - a common feed line, the common feed line having a common feed line inlet for receiving a fluid from a fluid source and at least one common feed line outlet, the received fluid forming a combined feed flow, the common feed line being adapted to transport said combined feed flow from the common feed line inlet to the common feed line outlet of outlets, - a plurality of reactor feed lines for receiving a reactor fluid flow, which reactor fluid flow is a part of the combined feed flow from the common feed line, and for transporting said reactor fluid flow to at least one of the plurality of reactors, each reactor feed line extending between a common feed line outlet and the reactor inlet of said reactor, - a measurement line, which measurement line has a plurality of measurement line outlets, each of the measurement line outlets connected to one of the reactor feed lines or to one of the reactors, and which measurement line has either one measurement line inlet that is connected to the common feed line or a plurality of measurement line inlets, each of those measurement line inlets being connected to one of the reactor feed lines, - in the measurement line, a first flow sensor for measuring the flow rate of the fluid flow through the measurement line, and - a valve system, comprising one or more valves and a valve control unit for controlling the one or more valves, the valve system being arranged and/or adapted such that it can assume a measurement setting in which the valves redirect one of the reactor feed flows such that it flows through the measurement line.