The presence of embedded steel affects the estimates obtained for the compressive strength of concrete during ultrasonic testing, as it increases the ultrasonic wave velocity. Thus, if the presence of steel in concrete is inevitable, then a correction factor is required for an accurate estimation of the concrete strength. While previous studies focused on the effect of steel reinforcing bars on the speed of ultrasonic waves in concrete, this work expands on the significance of embedded steel from steel bars to include steel plates. The wave velocity was measured for varying dimensions of embedded steel plates from 15 mm to 150 mm using 54-kHz ultrasonic testing equipment. Through experiments, the effect of steel plates on the ultrasonic testing of concrete was quantified to derive proper correction factors. It was found that the thickness, depth, and height of the steel plates significantly affected the test results. These findings can be applied to ultrasonic testing to estimate the compressive strength of concrete consisting of a significant volume of steel, such as in steel-reinforced concrete structures.