Pie Percent Game

About Pie Percent

Pie charts are everywhere: in news articles, budgets, reports and apps. This game asks you to read them the way a trained eye does, without labels or numbers. One slice is colored blue, the rest of the pie is gray, and you drag a slider to the percentage of the whole that you think the blue slice covers.

The early rounds are generous. The pie has one gray slice, the blue slice starts at the top or on a side, and the shares are round numbers like 25 or 75 percent. Later rounds rotate the chart to any starting angle, split the rest of the pie into several similar-looking pieces and, in many rounds, turn the pie into a donut with a hole in the middle, which removes the point where all slices meet.

How to play

1. Find the blue slice. Everything else in the chart is gray.
2. Compare it with the landmarks of a circle: a half is 50 percent, a quarter is 25 percent and an eighth is 12.5 percent.
3. Drag the slider to your estimate. The plus and minus buttons move it one percent at a time.
4. Lock in your answer. The true share appears as a marker on the slider, and your score shows how close you came.

One slice of the pie is highlighted. Drag the slider to the percentage of the whole pie that it covers.

How scoring works

The score is based on the absolute difference in percentage points. A perfect answer earns 100, and the points fall linearly to 0 at a tolerance of 22 points on level 1 and 10 points on level 10. On level 10, an answer that is 5 points off is worth about 50 points.

You have 12 seconds on the easiest level and 9 seconds on the hardest. If the timer runs out, the value on the slider is submitted at half score. The true share is always an integer, so a perfect score is realistic if you use the plus and minus buttons to fine-tune.

What it trains

Pie Percent trains proportion estimation, which means judging a part against a whole. Psychologists who study chart reading find that people rely on different cues here: the angle at the center, the area of the slice and the length of its arc. Practice teaches your eye to combine them.

The skill is useful whenever you read a chart or a diagram, split a bill, cut a cake, or check a progress ring on a phone. It also makes you a more critical reader of data, because you notice how a chart's design pulls on your judgment.

Tips for a higher score

• Use the quarter turns. Mentally draw a vertical and a horizontal line through the center. Slices that fill exactly one quadrant are 25 percent, and you can build up from there.
• Rotate in your head so the slice starts at 12 o'clock. A slice that ends at 3 o'clock is 25 percent, at 6 o'clock is 50 percent and at 9 o'clock is 75 percent.
• On a donut, imagine the hole filled in. The hole hides the center where angles are easiest to judge, so extend the edges of the slice inward to a point.
• Compare with the other slices. If the gray pieces are about equal and the blue slice is twice the size of one gray slice, you can reason about it as a ratio.
• Do not trust the size of the visible area alone. A thin slice at the edge looks smaller than the same angle drawn closer to the center of the pie.

The idea behind it

Studies of graphical perception, most famously by William Cleveland and Robert McGill in 1984, found that people judge positions along a common scale most accurately and angles and areas less accurately. Pie charts rely on angle and area, which helps explain why a bar chart is usually easier to read precisely.

That does not make pies useless. For simple part-to-whole comparisons, especially close to 25, 50 and 75 percent, people read them quickly and well. The game is a convenient way to see exactly where your own reading becomes unreliable.

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Free, no account. Your best scores are saved on your device.