The US system of units, also known as the Imperial system, is still commonly used in the United States for various measurements. When measuring weight, pounds are the standard unit, and they are often used in conjunction with ounces for smaller measurements.
A grand piano is a large and heavy musical instrument, so its weight is usually measured in pounds. The weight of a grand piano can vary depending on its size, make, and model, but it typically ranges from several hundred to over a thousand pounds.
Therefore, if you are using a scale to measure the weight of a grand piano in the US, it is most likely to display the weight in pounds.