Formulas, without the guesswork.
Choose a relationship from the measurements you know. The variable names below belong to each calculator; a letter can have a different role in another method. π is evaluated using the browser’s full numerical constant, rather than replacing it with 3.14.
From radius
Inputs: Radius r (length units).
From diameter
Inputs: Diameter d (length units).
From volume
Inputs: Volume V (cubic units).
From surface area
Inputs: Surface area S (square units).
Reading the notation
√ means a square root, ∛ means a cube root, and a superscript ² or ³ means a square or cube. Sine, cosine and tangent use angles converted from entered degrees. Where an inverse trigonometric function is used, its displayed angle is converted back to degrees. The ellipse perimeter is approximate; other formula labels describe the ideal mathematical model.
A hollow shell’s material volume requires an inner radius as well as an outer radius; this tool models a solid ball.
Reference reading: Sphere at Wolfram MathWorld.