Enter any two among perimeter, base and height (use consistent units), then click calculate to get the remaining one.
A parallelogram is a common quadrilateral whose opposite sides are parallel and equal. It appears frequently in structural design, layout planning and geometry problems.
If two adjacent sides are denoted by a and b, the perimeter formula is C = 2 × (a + b). In this tool, we treat “base” and “height” as the lengths of two adjacent sides and use this formula for calculation.
When perimeter C and one side are known, you can find the other side using a = C ÷ 2 − b or b = C ÷ 2 − a. When both side lengths are known, you can compute the perimeter from C = 2 × (a + b).
All inputs must be greater than zero, and half of the perimeter must be greater than each known side length; otherwise the given values cannot form a parallelogram that fits this model.
C = 2 × (a + b).
Opposite sides in a parallelogram are parallel and equal, but angles are not necessarily 90° as in a rectangle.
C = 2 × (5 + 8) = 26.
Half the perimeter is 20, so the other side is 20 − 9 = 11.
Because the formula links them directly; once two are known, the third is uniquely determined.
Yes. Perimeter, base and height must all use the same unit (e.g. all in cm).
It equals the sum of the two adjacent sides, a + b.
If C ÷ 2 is less than or equal to a known side length, the other side cannot be positive and the values are inconsistent.
For estimating fence length, layout design, structural planning, and geometry homework.
It is fast, avoids arithmetic mistakes and supports quick comparison of multiple input sets.
This tool lets you calculate the third value from any two of perimeter, base and height. Useful for geometry, design and engineering sketches.
Scan the QR code to use this tool on mobile.