Reading histograms, pie charts and dot plots

In Year 6 you learn three picture-style ways of showing data. Each one is good for a different kind of question.

Histogram

A histogram is a bar chart where the bars sit next to each other and the x-axis is a number line split into equal intervals (called bins).

The height of a bar tells you how many values fall into that bin.
All bins have the same width.

How to read it. Find the bin on the x-axis, then look up to the top of its bar. The height is the count.

Example: if the bin "10–20" has a bar of height 7, that means 7 values were between 10 and 20.

Pie chart

A pie chart shows how a whole is split into groups. The full circle is 100 % and each slice is a percentage.

Each slice's angle is its percentage of 360°.
The slices add up to 100 %.

How to read it. If you know the total count of the whole pie and a slice is, say, 25 %, then the count for that slice is

count = (percent × total) ÷ 100

Example. A pie chart of 200 votes shows a 25 % slice for blue. That slice represents 25 × 200 ÷ 100 = 50 votes.

Dot plot

A dot plot puts a number line on the x-axis and stacks one dot per measurement above the value it took.

Each dot is one piece of data.
The column with the most dots is the mode (most common value).

How to read it. To answer "how many dots above 5?", just count the dots stacked above the number 5. To find the total, count all the dots on the plot.

Quick checklist

Histogram? Find the bin → read the bar height.
Pie chart? Multiply the percent by the total and divide by 100.
Dot plot? Each dot is one measurement; count carefully.