I'm thinking of taking part in a cycling event, I'd like to do something that's about as challenging as running a half marathon (13 miles / 21 km). Approximately what distance should I be looking at?

I think in principal this could be worked out with a heart-rate monitor (if I had one):

  1. Walk or run for (say) 15 minutes, note the heart rate and the distance traveled
  2. Cycle for the same length of time with the same heart rate and note the distance traveled
  • 1
    Keep in mind that both require some ramp-up time (making side-by-side comparisons more difficult); a cyclist is likely to be a poor runner and vice-versa if they haven't cross-trained. My legs are reminding me of this right now--I can cycle at a good pace for well over 4-hours, but a very light 15 minute run on Saturday is still hurting.
    – STW
    Jul 25, 2011 at 20:23
  • Your question is unclear. What do you want to do? Ride a century? A half century? Or...do you want to know how to use a heart-rate monitor?
    – user313
    Jul 25, 2011 at 20:34
  • I'm not sure that the question is answerable. Cycling can be both "easier" or "more difficult". It really depends on the cycling.
    – user313
    Jul 29, 2011 at 0:27

7 Answers 7


I know calorie counts vary quite a bit, but a rough ballpark for cycling at a 20 mph pace is 450 calories per 15 minutes according to this calorie calculator.

Running a 6 minute mile is expected to burn a similar 450 calorie count on the same calculator with the same settings.

So, if you do the math, and the calculator is assumed to be reasonably accurate, then 5 miles on a bike at 20mph, is roughly equivalent to 1 mile run at a very fast pace.

Running a half marathon, which is 13 miles, and ignoring any difference due to endurance of effort, 13 miles at full pace running could be assumed to be a similar effort to 65 miles on a bike, in a very general sense.

This is dependent on fitness, body weight, and many other factors.

The best method to work it out would be to measure power expended, but I don't know how to do that for running, and to be accurate, you'd need to do it yourself, and for the full distance of the half marathon.

  • 3
    Yeah, that's about as accurate as you're going to get. My first thumb suck is that a marathon is about equal to a century, or maybe 120 miles, so a half-marathon would be 50-60 miles. And you can easily get 25% variation based on hills, road surface characteristics, and especially wind. (Remember, wind will affect the cyclist far more than the runner.) Jul 22, 2011 at 17:31
  • Yeah, that was my first guess, too. No way to really be accurate about it of course, short of serious lab work. Anybody want to sponsor an experiment? :)
    – zenbike
    Jul 22, 2011 at 17:35
  • When I try it that calorie calculator says only 255 calories / 15 minutes (for 150 lb, "racing extremely fast > 20 mph").
    – ChrisW
    Jul 23, 2011 at 2:13
  • @ChrisW: Try it at my weight. (110 Kg) That's why I said it was very dependent. Is the running similarly reduced?
    – zenbike
    Jul 23, 2011 at 3:15
  • 1
    Having done multiple editions of both, I would anecdotally say that running a marathon is way harder than a century but that would also be matched by the heart rate theory. Match heartrates and you'll be matching, basically, the output - but my marathon-running-pace heart rate is higher by 10-15 beats than my century-bike-pace (see first point). So it's not about the distance, it's about the perceived level of sustainable effort. Consider also the Ironman triathlon distance, while the swim is (comparatively) short, the 180km cycle matches the marathon run and I think are similar challenges.
    – Unsliced
    Jul 26, 2011 at 8:06

Cycling is different that running in that with cycling you can recover energy while riding and also expend far more amounts of energy when climbing that you do when running.

The rule of thumb in equivalence we talk about in our triathlon group is this:

1/2 marathon ~ 50 mile ride or metric century (100km/62 miles) depending on amount of climbs Full marathon ~ 100 mile ride

Cycling is much easier on the joints and rides usually have stops to eat, drink, pee, etc.

Cycling is harder than running when it comes to getting a good fit on the bike and getting flexibility in the different body parts to feel relaxed on the bike for hours on end.

Good luck!


The distance does not matter at all. What matters is the % of Heart Rate Max vs Time

The goal in training, whether running or cycling, is to achieve and maintain a specific HR range for some amount of time. That number is not directly related to distance.

Hypothetical example for a cyclist getting back into the swing after a winter of sloth...

  • March Riding for 30 minutes at 70% of HRMax - covered 15 miles
  • April Riding for 30 minutes at 70% of HRMax - covered 20 miles
  • May Riding for 30 minutes at 70% of HRMax - covered 25 miles

Distance is irrelevant. The idea is to think about intensity. At least for training/workouts. Otherwise it doesn't matter.

So getting back to the main question: How much easier is cycling compared to walking or running?

Way easier or can be. FWIW...my bike commute is far less effort than walking to work. That's why I do it. On the other hand, with intense interval training, one or two cycling miles can be quite difficult.


wdypdx22: how do you measure % of HRMax? Any cheap way to do that like approximating somehow while riding?

3 ways that I know of to determine Max Heart Rate:

  • Medical/sports medicine method - Involves a test in a lab either running on a treadmill or a cycling ergometer. The technicians will give you a number at the end. This is probably accurate, but, may be costly.
  • Various calculations - The original is - (Age - 220 = MHR). There are other, more modern calculations. You can find several variations here. Accuracy? It's a ballpark figure.
  • Functional methods - Basically, the idea is to ride very hard for "x" time (and perhaps more than once). Then, record your average and max HR. That way you have an idea of your MHR.

Another method is RPE (Rate of Perceived Exertion)

The goal, which is a % of the Max Heart Rate is easily calculated. No one needs my input.

  • wdypdx22: how do you measure % of HRMax? Any cheap way to do that like approximating somehow while riding?
    – user652
    Jul 26, 2011 at 19:02
  • Sorry I am confused with the middle part. "getting back into the swing"? I still upvoted +1 because this contain a good point, you can do anything "crazily" with high intensity :D
    – user652
    Jul 26, 2011 at 19:04
  • 1
    @hhhh - "getting back into the swing" means becoming reacquainted or reacclimatised or getting back into practice ... it's implied that people don't cycle during winter and become unfit/unused to exercise: that in May you can go 25 miles on a given amount of effort ('effort' measured as 'riding at 70% of your maximum heart rate for 30 minutes) whereas earlier in April you could only do 15 miles.
    – ChrisW
    Jul 27, 2011 at 2:48

We have all been cycling up a hill at a 'snail's pace' to be huffing and puffing, sweating out of every pore, with heart mouth, to pass pedestrians/joggers that are making good progress without showing any signs of being on the verge of a heart attack.

Arguably half-marathon by foot in flat terrain is going to be approximately as challenging as 13 miles cycled up an Alp. Therefore you are not able to compare apples and banana here, there is no distance or time comparison you can make. However, as a rule of thumb, cycling is four times as efficient as walking.

A lot of sportive events around here send you up and down the big hills and the hills with challenging gradients. Although there is a descent for every ascent you don't make up on the freewheeling what you lost on the agonising climb.

Some cycle events offer a variety of courses, you can sign up for the easy event and, part way through, if you are feeling good, take the full course loop.

The Wiggle 'Dragon' event in South Wales the other week has the difficult 'valleys' it also has the extended loop. The middle 120km distance in that terrain is more like your half marathon, the 200km more like your full marathon.

  • Good point about hills, I'd probably try and find a fairly flat event for my first one.
    – Tom77
    Jul 25, 2011 at 10:48

If I use the calculator at http://www.prohealth.com/weightloss/tools/exercise/calculator1_2.cfm at a weight of 165 lb then for bicycling at 14-16 mph "vigorous effort" it gives 750 calories/hour.

To spend 750 calories/hour running you need to run at 6mph (10 minute mile).

So at that level of effort (750 calories/hour), to run 12 miles would take 2 hours, during which time you could cycle 30 miles.

Personally I'd find the running more challenging.

  • I don't think 14-16mph is considered a "vigorous effort" of cycling. Jul 23, 2011 at 15:31
  • Looking at the calculator, that's right below "racing" which is at 20 mph. I checked Google and that's 32 km/h. I did a 70 km/h ride this spring, and I averaged around 30 km/h. And believe me, I wasn't "racing". I don't even have a high performance bike. A person in reasonable shape should be able to easily maintain 30 km/h on level roads with no wind, without a whole lot of effort.
    – Kibbee
    Jul 23, 2011 at 15:52
  • @ChrisW. I can sustain about 1000-1200 calories/hour for 20 minutes while using a stair-stepper or exercise bike at the gym. I can sustain 12-14 mph on level ground for about the same amount of time. I think the 750 cal/hour number is suspect. (Disclaimer -- I'm a 62 year old overweight male with post-polio.) Jul 23, 2011 at 17:01
  • The calorie calculation on gym exercise bikes and steppers is usually very optimistic to make the customer happy. The important thing is not the score though !
    – bobflux
    Jul 23, 2011 at 19:34

If you can run a half marathon, you probably have a nice endurance, that's good.

However different sports use different muscles in different ways. So, say you run a half marathon in a bit more than 1 hour...

If you do an effort of the same intensity (which is very intense) on a bicycle for an hour, and you're not used to cycling :

  • some of your muscles which are used to running and not to cycling will complain a lot
  • your ass will hurt like hell
  • your back, neck, arms etc will hurt too if the bike isn't adjusted properly to you (and to adjust it you need to ride for quite some time and touch up the settings until they're perfect)

So the only way to know is to try !

  • Yeah, I know I can cycle 80 miles on a good day. No way in Hades I could run 20, though. Jul 23, 2011 at 22:24

There is an excellent chart by R Chung in another question on this site How many miles of riding require the same effort as one mile of running?. His chart basically comes down to a ratio of 2.5 to 3.5. So if you are running at a speed of X per mile, then 13.1 miles of running is roughly equivalent to 32.75 to 45.85 miles or about 39.3 bicycle miles.


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