A parallelogram is a four-sided shape with two pairs of parallel sides. This calculator finds its area, perimeter, and diagonals from whichever measurements you already have — a base and height, or a base, side, and angle — without requiring you to work through the trigonometry by hand.
How the Parallelogram Calculator works
Area is computed with A = b·h whenever a height is available. If you only know a side length and the included angle instead, the calculator uses the equivalent formula A = a·b·sin(θ) — and internally derives a matching height (side × sin(θ)) so every tab stays consistent. Perimeter is simply P = 2(a+b), since opposite sides of a parallelogram are always equal. The two diagonals are found with the law of cosines, d² = a² + b² ∓ 2ab·cos(θ), applied to the triangle each diagonal forms with two adjacent sides.
Inputs and what they mean
Base is the one measurement every tab needs. Height must be the perpendicular distance to the opposite side, not the length of a slanted edge — mixing those up is the most common source of an incorrect area. Side is the length of an adjacent edge and is required for both the Perimeter and Diagonals tabs. The included angle is optional: leave it blank and the calculator derives it from height and side, or enter it directly if you measured the angle instead.
Limits and edge cases
When the included angle is 90°, the parallelogram is a rectangle and both diagonals come out equal — that's expected, not an error. If you only provide the base and height, the calculator can compute area but leaves perimeter and diagonals blank, since neither can be determined without a side length. A rhombus is the special case where the side equals the base (a = b); the same formulas apply unchanged.