In a circle, the area, the perimeter, the radius and the diameter are all related to each other. You can use the value of any one of these parameters to find out the value of the rest of them. Help your fourth grader learn the formulae for each of these circle parts with this printable math worksheet. Kids also learn how to use the formula in different ways by solving the practice problems provided. You can give your students extra practice with these concepts by using the other circle worksheets on our website.