How do you measure the size of a steel angle? A2: The size of a steel angle is measured by the length of its legs and the thickness. For example, an angle labeled 50x50x5 mm has two 50 mm legs and a thickness of 5 mm. https://medium.com/@marketingsteel6/ms-tmt-bar-prices-an-in-depth-guide-to-cost-and-purchasing-strategies-b72b9457db5a