Circle Graph Maker

Circle graph, pie chart, circle diagram

They're all the same thing: a circle split into parts that together make up a whole. American math classes tend to say "circle graph", offices say "pie chart", and some textbooks say "circle diagram" or "pie graph". Other languages have their own names too: diagram lingkaran in Indonesian, cirkeldiagram in Dutch, Kreisdiagramm in German, gráfico de pizza in Portuguese.

Whatever your assignment calls it, this tool makes it. The editor above starts with an example: how a student spends a school day, entered in hours.

Worked example: a school day in a circle graph

The usual homework version goes like this: turn each amount into a percentage, then into degrees, then draw. Here's the example from the editor, 24 hours in total:

1. Percent = hours ÷ total hours × 100. Sleep: 9 ÷ 24 × 100 = 37.5%.
2. Degrees = percent × 3.6, because the full circle is 360°. Sleep: 37.5 × 3.6 = 135°. With hours of a day there's a shortcut: each hour is 360 ÷ 24 = 15°, so 9 hours is 9 × 15 = 135°.
3. Check that the degrees add up to 360°. If you get 359° or 361°, it's rounding. Take the difference off the biggest part.

Drawing it by hand

1. Draw a circle with a compass and mark the center.
2. Draw one line from the center straight up to the edge. That's your starting line.
3. Put the protractor on the center, measure the first angle (135°) from the starting line and draw the next line.
4. Measure each next angle from the line you just drew. The last part should end exactly at your starting line.
5. Label every part with its name and percentage, and give the graph a title.

Then type the same numbers into the editor above. Chartty starts at 12 o'clock and goes clockwise, the same as the steps here, so you can hold your drawing next to the screen and compare.

When a circle graph is the wrong choice

• The parts don't make one whole. In a survey where each person could pick several answers, the percentages add up to more than 100%. Use a bar graph.
• You're showing change over time. Temperatures by month or sales by year belong in a line graph.
• There are too many parts. Past seven or so, the small parts become slivers. Combine them into "Other".