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 an edge
Inputs: Edge a (length units).
From volume
Inputs: Volume V (cubic units).
From height
Inputs: Height h (length units).
From total surface area
Inputs: Total 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.
These formulas require all six edges to be equal. A face altitude and the solid’s vertical height are different.
Reference reading: Regular tetrahedron at Wolfram MathWorld.