Is Japan’s Coastline Longer Than Australia’s?

May 30, 2014 at 8:00 am 2 comments

By Chad Upton | Editor-in-chief

I often come across the statement that Japan’s coastline is longer than Australia’s.

Although Australia has more than 20 times more land area than Japan, Japan actually has a longer coastline according to the World Factbook. The World Factbook, published by the CIA, lists Australia’s coastline at 25,760 km (16,007 miles) and Japan’s at 29,751 km (18,486 miles).


As you can see in the graphic above, Japan fits comfortably inside of Australia. So, how is it possible that it has a longer coastline?

Australia is mostly one large island (I know it’s not technically an island) with the majority of its land inside the coastal boundary. In comparison, Japan is made up of 6,852 islands and has a wildly meandering coastline. The meandering coastline brings up an interesting challenge when measuring coastlines: they’re not straight lines.

It’s easy to measure straight lines, the length is always the shortest distance from the beginning to the end. Measuring curved lines involved more complicated math. To simplify the problem, the curved lines are broken up into short straight lines that approximately represent the actual shape.

The fewer the lines, the easier the calculation:


Of course, fewer lines also means a less accurate measurement. You can see with more lines (more points of reference) the total length of the lines will be longer:


One potential problem with the CIA World Factbook is that we don’t know if the measurement of Japan and Australia’s coastlines were done with the same precision.

So, lets look at coastline data from the World Resources Institute, where we know the calculations of each coastline were made with a consistent level of precision. In that dataset, Australia’s coastline is more than double Japan’s. In that case Japan’s coastline is almost the same as the CIA Factbook at 29,020 km (18,032 miles) while Australia’s has jumped to 66,530 km (41,340 miles).

Australia’s coastline is almost triple the length using what we have to assume is a higher precision measurement.

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Sources: CIA (Japan, Australia), Wikipedia (Australia, Countries by Length of Coastline)

Entry filed under: Despite Popular Belief. Tags: , , , , , .

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2 Comments Add your own

  • 1. Kara Terna  |  January 22, 2015 at 3:11 am

    Well said, buddy to think that there’s thousands of people who would be fool for that “Fact” thanks for sharing.

  • 2. Nikhil  |  July 3, 2019 at 9:49 am

    Coastline Paradox


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