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.
Major and tube radii
Inputs: Major radius R (length units); Tube radius r (length units).
Outer radius and hole radius
Inputs: Outer radius (length units); Hole radius (length units).
Surface area and major radius
Inputs: Surface area S (square units); Major radius R (length units).
Volume and major radius
Inputs: Volume V (cubic units); Major radius R (length 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.
Major radius is not outer radius. All tools reject R ≤ r so that the result remains a ring torus.
Reference reading: Ring torus at Wolfram MathWorld.