The typical speed of sound in fat is approximately:

• A. 1600 m/s
• B. 1520 m/s
• C. 1450 m/s
• D. 1700 m/s

Answer: (C)

The speed of sound in a medium depends on how stiff it is and how dense it is—the stiffer the medium, the faster the wave travels; denser media tend to slow it down. Fat is less stiff than soft tissue, so waves move more slowly through fat. In practice, adipose tissue has a typical propagation speed of about 1450 m/s, which is slower than the around 1540 m/s usually cited for soft tissue.

So, 1450 m/s is the best match for fat. The other values align more with soft tissue or more dense tissues (higher speeds), not fat. This distinction matters in ultrasound when converting travel time to depth, since assuming the wrong speed can misestimate how deep a boundary lies.