An ultrasonic flow meter measures flow by timing sound pulses as they travel through the fluid. With no moving parts and no pressure loss, it has become a leading choice for large-diameter natural gas custody and pipeline measurement, where multipath designs governed by AGA Report No. 9 deliver high accuracy and wide rangeability.
Ultrasonic Flow Meter in one line: An ultrasonic flow meter measures flow from the difference in travel time of sound pulses sent with and against the flow: the faster the fluid, the greater the transit-time difference, which converts directly to velocity and volume.
A transit-time ultrasonic meter mounts pairs of transducers at an angle across the pipe. Each pair sends a sound pulse both upstream and downstream. A pulse traveling with the flow arrives faster than one traveling against it, and that difference in transit time is directly proportional to the fluid's velocity along the sound path. The meter converts path velocity to average pipe velocity and then to volumetric flow.
Because measurement is purely acoustic, there is nothing in the flow to wear out or obstruct it - no rotor, no plate, and negligible permanent pressure loss. Custody-grade gas meters use multiple acoustic paths (multipath meters) to sample the velocity profile across the pipe, which improves accuracy and tolerance to imperfect installation. The meter also reports the measured speed of sound, which is a valuable built-in diagnostic - a shift in speed of sound can flag a gas-composition change or a failing transducer.
For natural gas custody transfer, multipath ultrasonic meters are covered by AGA Report No. 9, which addresses design, performance, calibration, and diagnostics, with AGA 10 relating measured speed of sound to gas properties. They excel on large pipeline diameters and high volumes where an orifice plate's pressure loss would be costly, and their wide rangeability handles swinging flows well. Liquid ultrasonic meters serve crude and products service and are proved like other custody liquid meters.
A distinct advantage is diagnostics: multipath meters continuously report per-path performance, signal quality, gain, and speed of sound, which lets operators verify meter health between calibrations. The meter feeds a flow computer that applies pressure, temperature, and compressibility corrections and totalizes. That flow computer exposes rate, totals, and diagnostics over Modbus, so a cloud SCADA platform can trend flow and surface a path that has degraded before it affects the custody number. Clamp-on ultrasonic meters also exist for non-intrusive, temporary or check measurement, though they are generally not used for custody.
It times ultrasonic pulses sent both with and against the flow between angled transducers. Flow speeds up the downstream pulse and slows the upstream one, and that transit-time difference is proportional to fluid velocity. Converting velocity to volumetric flow needs only the geometry - nothing physically spins or obstructs the stream.
A multipath meter uses several acoustic paths at different positions across the pipe instead of one. Sampling the velocity at multiple chords gives a far better estimate of the true average velocity, improving accuracy and reducing sensitivity to a distorted flow profile. Custody-grade gas ultrasonic meters under AGA 9 are multipath for this reason.
The meter measures the speed of sound in the gas as a by-product. That value depends on gas composition, temperature, and pressure, so an unexpected shift can flag a change in gas quality or a transducer beginning to fail. Comparing measured speed of sound to a value computed from composition (per AGA 10) is a standard meter-health check.
This page references the protocol specifications published by the organizations below. Editions, product capabilities, and documentation change over time - confirm current requirements and specifications directly with the source.
Last reviewed: July 27, 2026. Merobix is not affiliated with, endorsed by, or sponsored by these organizations; their names are used only to identify the standards and products discussed.
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