Stand at the edge of the bathtub and spread the measuring tape across the tub width-wise. Write down this measurement.
Place the measuring tape on one end of the tub and pull it lengthwise to the other end of the tub. Write down this measurement.
Hold the measuring tape at one end of the opening of the bathtub, and pull the measuring tape to the other end of the bathtub opening width-wise and lengthwise to measure how large the inside of the tub is. Write down both of these measurements.
Hold the measuring tape at the top of the tub and pull it to the ground to measure the height of the tub. Write down this measurement.