The Eddington Number

I stopped working about three years ago.  I’ve stayed reasonably healthy since then too.  Not falling off my bicycle has helped in that regard.  Time and health have allowed me to aim to ride at least 12,000km / 7,456mi per year.  Which I did in 2016 and 2017.  I’m delighted to say that I am on track to do the same in 2018.

Tracking how far I ride has introduced me to the Eddington Number.  Sir Arthur Stanley Eddington was a noted British astrophysicist, making fundamental contributions to our understanding of general relativity, as well as the internal structure of stars and the method by which they generate energy.

He was also an avid cyclist.  He devised a method of measuring long-distance cycling achievements, now known as the Eddington Number (E number).  This is defined as:

The largest integer n such that one had cycled at least n miles on n different days.

For example, if you have ridden 25 miles on 25 days, your E number is 25.  If you have ridden 30 miles on 30 different days, your E number is 30.  As your E number gets bigger, it becomes progressively more difficult to further increase your number.  Not all the rides contributing to your current E number will count towards the next one.

As I live in a metric country, I measure my E number using kilometres instead of miles.  The downside of this is that it takes more days to get to a particular E number in kilometres than it does to get to the equivalent E number in miles.

An imperial E number of 50 means having ridden at least 50 miles on 50 days.  50 miles converts to 80 kilometres. The metric E number equivalent means having ridden at least 80 kilometres on 80 different days.

Whether imperial or metric, tracking your E number online requires that you use Strava to record your ride data.  A number of websites link to your Strava data to calculate your E number.

I use Veloviewer at

The Veloviewer Summary page lists a variety of Activity Stats, including your E number in miles and kilometres.  Clicking on the Eddington button open up a more detailed graph.

Graph courtesy of Veloviewer

Another option is at

A third option is at the University of Cambridge custom-built Eddington Number challenge site at

Note that the Cambridge University campaign runs until September.  I do not know if their site will remain live after the end of the campaign.

My annual distance goal is my main cycling challenge.  Increasing my E number is a more passive challenge.  Until I get to within a day or two of moving it up one notch.  At which point riding the required distance becomes a goal in itself!

If you want a new cycling challenge, the Eddington Number is a good one.

You can read my 2017 blog post about the Eddington Number and how Veloviewer displays it here.

7 response to "The Eddington Number"

  1. By: Bill Stone Posted: August 10, 2018

    I’m a little uncertain about the E number. Is the maximum annual E number 366? That is, 366 days of riding at least 366 miles each day (in a leap year). I don’t expect to achieve that!

    • By: Alchemyrider Posted: August 10, 2018

      Hi Bill. The E number is not time limited. So it is a lifetime challenge as oppose to an annual challenge.

    • By: Alchemyrider Posted: August 10, 2018

      The better answer is that you can set your own time parameter for your E number. I’ve read about people who have an annual goal. Which as you say cannot be more that 366.

      • By: Bill Stone Posted: August 11, 2018

        I had not previously heard of the E number. Very interesting. Thanks for introducing me to it.

  2. By: Rich-Illinois Posted: August 11, 2018

    That is a LOT of miles! Not falling off our bicycles is always a good thing! 🙂
    Very doubtful my E number will ever exceed 10.
    (Took a while for that info to soak into this impervious noggin)

    Wikipedia states that Eddington’s own E number was 84!

  3. By: Gary Lee Posted: August 11, 2018

    Thank you for introducing the E number. My life time figure is only 57 (Metric) which still have room for improvement.

  4. By: Seasidejanet Posted: August 11, 2018

    Jack is a solid 20 …… always I’m still trying to figure me out. Way to many variables😂😂 Always fun to learn something new.

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