Ellipse Circumference Calculator

What is Ellipse Circumference?

Unlike a circle, an ellipse has no exact elementary formula for its perimeter. Ramanujan's approximation is the standard friendly formula, accurate to better than 0.01% for most ellipses.

How it works

We compute the flattening term h = (a−b)²/(a+b)² and apply C ≈ π(a+b)(1 + 3h/(10 + √(4−3h))). The result is labelled an approximation rather than presented as exact.

1. Enter your input. Type or paste your input into the field above — the tool responds instantly.
2. Review the result. Output updates live as you type. Everything runs entirely in your browser.
3. Copy or download. Use the Copy button to grab the result, or Download to save it as a file.

Examples

Realistic sample

Type or paste any realistic input — the tool computes the result locally and instantly.

Common mistakes

Expecting a server round-trip

Nothing is uploaded — every tool in this category runs entirely in your browser.