To manufacture different types of sheet metal components with variety of sizes and shapes used in the automobile industry, appliances, aerospace industry, etc., in large volume a conventional sheet metal forming process such as stamping, drawing, coining, blanking, etc., methods are used. However for producing small quantity of products the cost of production is higher. Therefore, an Incremental sheet metal forming (ISF) is used to produce three-dimensional elements from metal sheets using minimal tools and fixtures. Studying impact of different process parameters of ISF is a very important theme. In present work, a systematic study on the effect of tool diameter (8, 10, 12, 14, and 16 mm) on sheet thinning in Single point incremental forming of AA-1050 was done using a finite element analysis. A detailed comparison of sheet thinning and formability was compared for different tool diameters. It was observed that sheet thinning increases with an increase in tool diameter.