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.
Triangular base sides and prism length
Inputs: Base side a (length units); Base side b (length units); Base side c (length units); Prism length L (length units).
Right-triangle base and prism length
Inputs: Base leg a (length units); Base leg b (length units); Prism length L (length units).
Base area, base perimeter and prism length
Inputs: Base area (square units); Base perimeter (length units); Prism length L (length units).
Volume and triangular base sides
Inputs: Volume V (cubic units); Base side a (length units); Base side b (length units); Base side c (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.
A triangle’s altitude and the prism’s length are distinct. Oblique prisms require a different treatment of lateral surface area.
Reference reading: Right triangular prism at Wolfram MathWorld.