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.
Three perpendicular edges
Inputs: Length a (length units); Width b (length units); Height c (length units).
Volume and two edges
Inputs: Volume V (cubic units); Length a (length units); Width b (length units).
Surface area and two edges
Inputs: Total surface area S (square units); Length a (length units); Width b (length units).
Space diagonal and two edges
Inputs: Space diagonal d (length units); Length a (length units); Width b (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.
Internal capacity and external dimensions differ for a box with thick walls. Choose one consistent measurement convention.
Reference reading: Cuboid at Wolfram MathWorld.