Draw a perfect circle in one stroke. The Kasa circle-fitting algorithm scores your attempt from 0 to 100%.

Perfect Circle is a minimalist skill game where you draw a circle in a single uninterrupted stroke using your mouse or finger. The moment you release the pointer, a Kasa circle-fitting algorithm computes the best-fit circle through your points and returns an accuracy score from 0% to 100% based on the root-mean-square deviation. No sign-up is required, results appear instantly, and you can share a result card with friends to see who can draw the roundest circle.

The trick to a high score is speed control and consistency. Sweeping too fast almost always produces an oval, so slow down and keep the pointer moving at an even pace along the arc. Pivot from your wrist or even your elbow rather than dragging from your fingertips — a fixed rotation axis naturally generates a smoother curve. Pick an imaginary center on the canvas and try to keep an identical distance from it the whole way around. Starting and ending points don't need to meet exactly, but the stroke should flow in one breath without hesitation.

Humans are notoriously bad at freehand circles. Art schools teach big shoulder-driven circles as a warm-up for motor coordination, and some neuropsychological assessments use circle-drawing as a quick proxy for fine motor control. Reliably scoring above 99% usually takes dozens of attempts, which is part of why the challenge is so addictive.

FAQ — Q. Does it work on mobile? A. Yes, touch drag works identically to a mouse. Q. Why is my score so low? A. Drawing too small inflates the relative pixel error; aim for roughly half the canvas width. Q. Can I share the result? A. Yes, the page generates a card with your circle and score that you can share to KakaoTalk and other social platforms.