What is voter turnout?

Suppose a house has 4 people – 2 adults and 2 children under the age of 18. Only the 2 adults in this house can vote. This means that there are 2 eligible voters. 

Now, lets suppose that only one of them actually goes to the polling booth to vote. Out of 2 people who should have voted, 

only one turned up to vote. 

The voter turnout is: 

No. of people who turned up to vote 

No. of people who should have turned up to vote 

In our case, it becomes 1/2 = 50% 

Now, suppose a city has 1000 citizens. But only 800 of them are above the age of 18. 

So the number of eligible voters is 800. 

On the day of the election, 600 of them come to the polling booth and cast their vote. 

The turnout on this day is: 

600 / 800 = 75% 

In short, voter turnout is the number of people who actually turn up to vote.