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Perfect Circle Tips: How the Roundness Score Really Works

Updated October 2026

Perfect Circle looks like the simplest test on the site: draw one loop, lift your finger, read a percentage. Yet most players stall somewhere in the 80s and cannot say why, because the score is not judging what they think it is judging. This guide walks through the exact calculation the game runs when you lift your finger, the conditions that make a stroke count at all, and the habits that move a drawing from "Great" into the 90s. Several numbers below come from our own simulation of the scoring code, and they are labelled that way.

What the game actually measures

While your finger moves, the game records a point each time it has travelled at least 2 pixels from the previous one, including the in-between positions that fast screens report between frames. When you let go, it first trims any overlap: if you went past your starting point, the stroke is cut where it came closest to the start. It then lays 96 measuring points along the line at equal spacing, smoothing between the recorded points, and finds the circle that best fits those 96 points. Every measuring point's distance from that fitted centre is taken; the average distance is your radius, and the spread of the distances around that average is what decides the score.

Specifically, the game divides the standard deviation of the distances by the average radius, multiplies that ratio by 3.2, and subtracts the result from 100 percent, shown to one decimal place. A spread of 1 percent of the radius therefore costs about 3.2 points, and a spread of 10 percent costs 32. Working backwards gives these targets:

Because everything is measured relative to the radius, a 3-pixel wobble matters half as much on a big circle as on a small one. In our simulation, a ring with a 3-pixel ripple scored 94.4 at a radius of 120 pixels but only 88.9 at a radius of 60.

When a stroke does not count

Four checks run before any scoring. A stroke with fewer than 18 recorded points is rejected outright. A drawing whose average radius is under 40 pixels is rejected as too small. A stroke that never comes back within half a radius of its first point is treated as an open arc; half a radius along the rim works out to roughly 29 degrees, so you must get back within about that angle of where you started. Going past the start is fine, because the overlap is trimmed off. Finally, the grey dot has to be in the middle: if the centre of the fitted circle lies more than a quarter of the radius away from the dot, the attempt does not count.

A rejected stroke shows no percentage. The prompt changes to "Keep the dot in the middle of your circle" if the loop was off-centre, and to "Draw a bigger, closed circle" if it was too short, too small or too open. Nothing is lost; touch the screen again and start over.

A quarter of the radius is a generous allowance on a big loop: about 30 pixels at a radius of 120. Treat the dot as the pivot of your motion and the check will rarely bite.

Speed does not matter, and why

Earlier versions of the game found the centre by averaging the raw recorded points, so wherever your finger slowed down, the cluster of extra points dragged the centre toward it and a perfectly round loop scored as lopsided. A faster screen, which reports more positions per second, also scored higher than a 60 Hz one. That is gone. Because the measuring points are laid out evenly along the line itself, it no longer matters how quickly your finger covered any part of it.

In our simulation of the current scoring code, a mathematically perfect circle scored 100.0 whether it was drawn at an even pace or twice as fast on one side as on the other, at 60 or 120 position reports per second, and in 0.3, one or two seconds (99.5 for the 0.3-second sweep at 60 reports per second, where there are barely enough points).

So choose your pace for control, not for the scorer. Hesitations still matter if they make your line wobble or bend, because that changes the shape, but simply slowing down in one place costs nothing. Most people find a loop of one to two seconds easiest to keep round.

Shape errors and what they cost

Since only the shape counts, the faults to fix are shape faults. The two common ones are ovals and drifting radius.

After each valid attempt the game paints your stroke in a colour (green from 85, orange from 60, red below) and lays a dashed white reference circle over it, with a small dot at the computed centre. Look at where your line sits outside the dashed ring and where it sits inside. Bulges on the left and right with flat top and bottom mean an oval; a line that starts outside and ends inside means a spiral.

Closing the loop cleanly

The end of the stroke is about getting back to the start, not about stopping on an exact spot. If you overshoot, the game cuts the stroke where it came closest to your starting point, so the overlap is not counted twice; in our simulation a perfect loop scored 100.0 with an overshoot of 10, 20 or even 40 degrees. Stopping short is also fine up to about 29 degrees, beyond which the stroke is rejected as open.

The practical rule: carry the loop all the way round and a little past the start rather than braking early, and lift your finger cleanly. A small overrun is free; a gap that is too large is not.

Posture and technique

Size the loop to fill most of the drawing area while leaving a margin at the edges; a bigger radius makes every pixel of wobble cheaper, but loops that run into the screen edge flatten. Hold the phone steady on a table or in your other hand so that only the drawing finger moves. Rotating from the wrist or elbow, with the fingertip held still relative to the hand, gives a more even radius than walking the fingertip around.

Start at a point where your hand feels most comfortable, often the bottom or the left side for a right-handed player, so the awkward part of the loop falls in the middle of the stroke when your motion is already flowing.

A practice routine

  1. Draw five loops at a pace that feels comfortable, and only watch the dashed ring for oval or spiral patterns.
  2. Draw five more at the same size with your wrist or elbow planted, keeping the dot under the pivot of the motion.
  3. Practise the finish: carry the loop a little past the start point and lift straight off.
  4. Once you are regularly above 90, save a good attempt from the result card. Each card's save button stores that attempt's score; your local best is kept on the device either way.

There is no timer and no limit on attempts, and touching the screen again simply starts a new loop. Treat every attempt as data: one change at a time, checked against the reference ring.

▶ Play Perfect Circle One finger, one loop, one percentage.