A venturi flow sensing method, system, and apparatus. A tube or chamber may be tapered from a larger to smaller diameter to create a venturi region within the tube or chamber. The venturi region causes a local increase in flow velocity. The change in velocity creates a local change in pressure which is, in turn, used to drive flow through a parallel bypass tube or chamber. Inside this bypass, a flow sensor can be located, and in some cases, a pressure sensor as well. The flow is then either exhausted back into the original tube or the bypass tube may alternatively dead end. In either case, flow can be measured without causing a significant overall pressure drop in the system.