What is the difference between long/short diameters and semi-axes?

The long and short diameters are the full end-to-end measurements across the oval. The semi-major axis a and semi-minor axis b are half of those values, measured from the center to the edge. If you enter diameters, the calculator quietly converts them with a = major / 2 and b = minor / 2 before solving the ellipse.

Yes, if your shape is an ellipse. The area formula A = piab is exact for an ellipse, so once the semi-major and semi-minor axes are known, the area is exact geometry.

Why is the perimeter labeled as approximate?

Unlike the area, ellipse perimeter does not collapse to a simple exact formula in elementary terms. This calculator uses Ramanujan’s well-known approximation, which is practical for planning cover edge, trim, or garden-bed border material without pretending to be fabrication-grade precision.

What unit should I use?

Any consistent length unit works: meters, centimeters, feet, or inches. Keep both measurements in the same unit. The area result is shown in squared units, while the perimeter stays in the original linear unit.

When should I use this instead of a circle or rectangle calculator?

Use this when the shape is genuinely oval. Circle formulas assume one radius everywhere, and rectangle formulas assume straight edges with square corners. If you are measuring an oval pool, rug, tabletop, or planting outline, ellipse math is the closer match.

Oval Area Calculator

Measure the long way and the short way of an oval pool, rug, tabletop, or garden bed, then get the enclosed area plus the edging length you need for covers, trim, or border material.

How It Works

Formula

A = \pi ab

a = \frac{\text{major diameter}}{2}

b = \frac{\text{minor diameter}}{2}

P \approx \pi(a+b)\left(1 + \frac{3h}{10 + \sqrt{4 - 3h}}\right)

h = \left(\frac{a-b}{a+b}\right)^2

Choose whether you measured full diameters or already know the semi-axes. In diameter mode, the calculator first converts the long and short dimensions into a = major / 2 and b = minor / 2. It then computes the exact ellipse area with A = piab. For edging length, it uses Ramanujan’s ellipse-perimeter approximation so you can estimate border, trim, or cover-edge material without confusing that estimate with precision fabrication geometry.

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