Circumference of a circle = diameter X 3.1416 Area of a circle = square of the radius X 3.1416 Area of a circle = square of the diameter X 0.7854 Area of a circle = square of the circumference X 0.07958 Area of a circle = half the circumference X half the diameter Radius of a circle = circumference X 0.159155 Radius of a circle = square root of the area X 0.56419 Diameter of a circle = circumference X 0.31831 Diameter of a circle = square root of area X 1.12838 Side of an inscribed square = diameter X 0.7071 Side of an inscribed square = circumference X 0.2251 Side of an equal square = diameter X 0.8862 Area of a triangle = base by 1/2 the altitude
 Area of an ellipse = product of both diameters X .7854 Surface of a sphere = circumference X diameter Surface of a sphere = square of the diameter X 3.1416 Surface of a sphere = square of the circumference X 0.3183 Solid contents of a sphere = surface X 1/16 of its diameter Solid contents of a sphere = cube of diameter X 0.5236 Diameter of a sphere = square root of surface X 0.56419 Diameter of a sphere = cube root of solidity X 1.2407 Circumference of a sphere = cube root of solidity X 3.8978 Solid contents of a cone or pyramid = area of base X 1/3 altitude Surface of a cube = six X area of one side Area of trapezoid = altitude X 1/2 sum of parallel sides

Note - Volumes of similar solids are to each other as the cubes of their similar lines.