It’s 42.195.
That’s the number. If you were just looking for the quick answer to how long is a marathon in km, there it is. But honestly, if you stop there, you’re missing out on one of the most chaotic, accidental, and strangely royal stories in the history of modern athletics. Most people assume there’s some deep, scientific reason for that specific decimal point. Maybe it’s the exact distance from an ancient Greek battlefield to Athens? Nope.
The real story involves a bunch of British royals who didn't want to get their shoes wet and a finish line moved specifically so some kids could watch the race from a nursery window.
Seriously.
The Greek Myth vs. The Olympic Reality
Let's clear the air. Everyone knows the legend of Pheidippides. The story goes that in 490 BCE, a Greek messenger ran from the Battle of Marathon all the way to Athens to shout "Niki!" (Victory!) and then promptly dropped dead. It’s dramatic. It’s inspiring. It’s also probably a bit of a stretch, according to historians like Herodotus. Even if it happened, the distance between those two points isn't 42.195 kilometers. It’s closer to 40 kilometers.
When the first modern Olympics kicked off in 1896, they used that 40km figure. It was a nice, round number. It felt "historical enough." For the next few Games, the distance was basically "whatever feels right for the local geography." In 1900, it was 40.26 km. In 1904, it was 39.06 km. Nobody really cared about precision because the marathon was more about the grueling survival of the distance rather than chasing a world record.
Then came London in 1908.
How a Royal Nursery Changed the World Record
If you’re wondering why how long is a marathon in km ended up being such a messy number, you can thank King Edward VII.
The 1908 London Olympic marathon was originally supposed to be 26 miles (41.8 km). The start was planned at Windsor Castle and the finish at the White City Stadium. Simple, right? But the Queen wanted the race to start on the lawn of Windsor Castle so the royal grandchildren could watch from the nursery. Then, to make sure the finish line was directly in front of the Royal Box at the stadium, they tacked on an extra 385 yards.
That random adjustment created the 26 miles and 385 yards standard.
It took another 13 years for the International Amateur Athletic Federation (IAAF) to sit down and say, "Okay, we need to pick one distance and stick to it." They looked back at the 1908 race—which was incredibly dramatic and popular—and decided that the London distance would be the official standard forever. They converted those miles and yards into the metric system, and we ended up with exactly 42.195 km.
It’s a weirdly specific number born out of British logistical convenience.
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Why That Extra 195 Meters Is a Psychological Nightmare
Ask any runner. Those last 195 meters are the longest part of the race.
By the time you hit the 42km mark, your body has usually run out of glycogen. This is "The Wall." You’re moving on fumes and sheer stubbornness. 42 kilometers is a massive achievement, but that final 0.195 km—less than half a lap of a standard track—is where the real mental battle happens.
Think about the physiology for a second. Most people can store enough fuel (glycogen) in their muscles and liver to last about 30 to 35 kilometers. After that, your body starts trying to burn fat for energy, which is a much slower process. It feels like your legs have been replaced with concrete blocks. If the marathon had stayed at the original Greek distance of 40km, "The Wall" wouldn't be nearly as legendary as it is today.
Precision Matters: The Jones Counter
You can't just measure a marathon with a car's odometer or a basic GPS watch. If you use your Garmin to run a marathon, it will almost certainly tell you that you ran 42.5 or 43 kilometers. This is because GPS isn't perfect, and you likely didn't run the "tangents" (the shortest possible line around every curve).
To ensure the distance is exactly 42.195 km, official courses are measured using the Shortest Possible Route (SPR).
Measurers use a device called a Jones Counter, which is a mechanical gear-driven counter attached to a bicycle wheel. They calibrate the bike on a strictly measured 1,000-meter stretch of road and then ride the entire marathon course, hugging every curb and cutting every corner. They even add a "Short Course Prevention Factor" of 0.1%. This means they intentionally make the course 42 meters longer than 42.195 km just to guarantee it isn't a single centimeter too short.
If a course is even an inch short, any world record set on it is void. Just ask the organizers of the 2022 Brighton Marathon, who accidentally set the course 568 meters too long. Or worse, the 1981 New York City Marathon, which was found to be 150 yards short years after Alberto Salazar set what he thought was a world record.
Beyond the Standard Distance
While 42.195 km is the standard, the world of long-distance running has exploded into variants:
- The Half Marathon: Exactly 21.0975 km. This is the "gateway drug" for most runners.
- Ultramarathons: Anything longer than a marathon. Common distances are 50 km, 100 km, or even 161 km (the classic 100-miler).
- The Boston Exception: The Boston Marathon is 42.195 km, but it isn't "record-eligible" because it’s a point-to-point course with too much net downhill. If someone runs a world-best time there, the history books put an asterisk next to it.
The marathon is a strange beast. It’s a distance that's long enough to require months of training but short enough that the elites can sprint the whole thing. Eliud Kipchoge, the first human to run the distance in under two hours (though in a non-competitive, optimized setting), averaged a pace of about 2:50 per kilometer.
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Think about that.
Try running a single kilometer in 2 minutes and 50 seconds. Most people can't do it once. Kipchoge did it forty-two times in a row, plus that final 195-meter kick.
How to Prepare for Your Own 42.195 km
If you're planning to tackle the 42.195 km distance, don't just lace up and go. You’ll get hurt.
Most training plans are 16 to 20 weeks long. You start with "base building"—low-intensity miles to get your heart and joints ready. Then you move into long runs, which gradually increase until you’re hitting 30 or 32 km in a single session. You rarely run the full 42.195 km in training because the recovery time is too high. You save that final 10km for race day, fueled by adrenaline and the crowds.
Nutrition is the "fourth discipline." You have to train your gut to take in carbs while you're running. If you don't, you hit the wall. Hard. We're talking gels, chews, and sports drinks every 45 minutes.
Actionable Next Steps for Aspiring Marathoners
If you’re serious about moving from "knowing the distance" to "covering the distance," here is your immediate checklist:
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- Get Fitted for Shoes: Go to a dedicated running store. Don't buy what looks cool. Buy what supports your gait. A marathon in the wrong shoes will cost you your toenails.
- Pick a Race 6 Months Out: You need a goal. Don't pick a "hilly" one for your first time. Look for a flat, "PR-friendly" course.
- Focus on Minutes, Not Miles: In the first month, just focus on moving for 30 minutes, three times a week. Don't worry about the kilometer count yet.
- Join a Local Run Club: The 42.195 km journey is lonely. Having a group for the Sunday long runs makes the distance feel like 10km instead of a marathon.
- Download a Real Plan: Use a reputable source like Hal Higdon or Pfitzinger. Random "get fit" apps usually lack the specific periodization needed to avoid injury.
The marathon isn't just a number. It's a 120-year-old accident of British royalty that has become the ultimate benchmark of human endurance. Whether you're running it in two hours or seven, those 42.195 kilometers will change how you look at what your body can do.