A system for pressure-based flow measurement of a fluid flow, the system comprising: a pressure-based mass flow controller, MFC, including a flow control valve, a flow restrictor, and a pressure sensor upstream of the flow restrictor, wherein the flow control valve, flow restrictor and pressure sensor are disposed along a flow stream; one or more processors (140, 600) coupled with the pressure-based mass flow controller, MFC; and memory coupled to the one or more processors, the memory including instructions which, when executed by the one or more processors, cause the one or more processors to: (i) receive, from the pressure-based mass flow controller, MFC, an upstream pressure value P u (705, 815) measured by the pressure sensor; (ii) calculate, for the pressure-based mass flow controller, MFC, a downstream pressure value P d based on the received upstream pressure value P u; (iii) calculate, for the pressure-based mass flow controller, MFC, a flow rate Q based on the received upstream pressure value P u and the calculated downstream pressure value P d; and (iv) control a flow through the pressure-based mass flow controller, MFC, based on the calculated flow rate Q (720, 840); where the instructions to calculate the downstream pressure P d and the instructions to calculate the flow rate Q include: instructions to set P d to an initial value P do; and instructions to recursively calculate the flow rate Q and P d until the values of Q and P d converge within a pre-defined error threshold, including instructions to receive, from the pressure-based mass flow controller, MFC, an updated upstream pressure value P u; and determine, based on P d and P u, whether a flow condition in the pressure-based mass flow controller, MFC is critical or non-critical flow; and calculate Q based on whether the flow condition is critical or non-critical flow; and update P d based on the calculated value of Q. a pressure-based mass flow controller, MFC, including a flow control valve, a flow restrictor, and a pressure sensor upstream of the flow restrictor, wherein the flow control valve, flow restrictor and pressure sensor are disposed along a flow stream; one or more processors (140, 600) coupled with the pressure-based mass flow controller, MFC; and memory coupled to the one or more processors, the memory including instructions which, when executed by the one or more processors, cause the one or more processors to: (i) receive, from the pressure-based mass flow controller, MFC, an upstream pressure value P u (705, 815) measured by the pressure sensor; (ii) calculate, for the pressure-based mass flow controller, MFC, a downstream pressure value P d based on the received upstream pressure value P u; (iii) calculate, for the pressure-based mass flow controller, MFC, a flow rate Q based on the received upstream pressure value P u and the calculated downstream pressure value P d; and (iv) control a flow through the pressure-based mass flow controller, MFC, based on the calculated flow rate Q (720, 840); (i) receive, from the pressure-based mass flow controller, MFC, an upstream pressure value P u (705, 815) measured by the pressure sensor; (ii) calculate, for the pressure-based mass flow controller, MFC, a downstream pressure value P d based on the received upstream pressure value P u; (iii) calculate, for the pressure-based mass flow controller, MFC, a flow rate Q based on the received upstream pressure value P u and the calculated downstream pressure value P d; and (iv) control a flow through the pressure-based mass flow controller, MFC, based on the calculated flow rate Q (720, 840); where the instructions to calculate the downstream pressure P d and the instructions to calculate the flow rate Q include: instructions to set P d to an initial value P do; and instructions to recursively calculate the flow rate Q and P d until the values of Q and P d converge within a pre-defined error threshold, including instructions to receive, from the pressure-based mass flow controller, MFC, an updated upstream pressure value P u; and determine, based on P d and P u, whether a flow condition in the pressure-based mass flow controller, MFC is critical or non-critical flow; and calculate Q based on whether the flow condition is critical or non-critical flow; and update P d based on the calculated value of Q. instructions to set P d to an initial value P do; and instructions to recursively calculate the flow rate Q and P d until the values of Q and P d converge within a pre-defined error threshold, including instructions to receive, from the pressure-based mass flow controller, MFC, an updated upstream pressure value P u; and determine, based on P d and P u, whether a flow condition in the pressure-based mass flow controller, MFC is critical or non-critical flow; and calculate Q based on whether the flow condition is critical or non-critical flow; and update P d based on the calculated value of Q.