You're standing at the start line. Your heart is thumping against your ribs like a trapped bird, and the air smells like a mix of tiger balm and nervous sweat. You know you're about to run a long way. But exactly how many km in a marathon are you actually signed up for?
It’s 42.195 kilometers.
That number is weird. It’s not a round 40 or a clean 45. It’s specific, jagged, and honestly, those last 195 meters feel like a cruel joke when your quads are screaming at you to stop. If you’ve ever wondered why we don’t just call it an even 42, you have to look back at a very particular British royal request from 1908. Before that, distances were all over the map.
The messy history of the distance
Most people think the marathon comes from the legend of Pheidippides. The story goes that he ran from the battlefield of Marathon to Athens to announce a Greek victory. He yelled "We have won!" and then dropped dead. It’s a great story. It’s also probably not true, or at least heavily embellished by historians like Herodotus.
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In the first modern Olympics in 1896, the distance was roughly 40 kilometers. That was basically the distance from the Marathon bridge to the Olympic stadium. But back then, nobody was obsessed with "standardization" yet. Race organizers just picked a distance that seemed "long enough."
Then came the London Olympics in 1908. This is where the 42.195 km in a marathon became the law of the land.
The race was supposed to start at Windsor Castle and finish at the White City Stadium. Originally, it was meant to be 26 miles. But the Royal Family wanted the race to start under the windows of the Nursery at Windsor Castle so the kids could watch. Then, they wanted it to finish right in front of the Royal Box at the stadium.
Those extra bits added up.
By the time they measured the detours for the Queen and the kids, the distance landed on 26 miles and 385 yards. In metric terms? That’s 42.195 km. It took until 1921 for the International Amateur Athletic Federation (IAAF) to officially bake this specific number into the rulebook.
Breaking down the 42.195 km journey
Running this distance isn't just about moving your legs. It's a physiological war. Most runners divide the km in a marathon into segments, because looking at the whole 42 at once is mentally paralyzing.
The first 10 km are a trap. You feel amazing. The "taper crazies" have left you with way too much energy, and the crowd is screaming. You'll likely go too fast. Experts like coach Jack Daniels often warn that "banking time" in the first 10k is a recipe for disaster. If you're running faster than your goal pace here, you're just burning the matches you'll need at km 35.
By the time you hit the halfway mark at 21.0975 km, reality sets in.
The "Wall" usually waits for you around km 30 or 32. This isn't just a mental thing; it's biology. Your body stores about 2,000 calories worth of glycogen in your muscles and liver. For most humans, that fuel tank runs dry right around the 30 km mark. When the glycogen is gone, your body starts trying to burn fat for fuel, which is a much slower, less efficient process. It feels like someone replaced your blood with lead.
Why GPS watches almost always say you ran more
If you finish a race and your Garmin says 42.6 km, don't sue the race director. You didn't get cheated. Well, you did run extra, but it's your fault, not theirs.
Courses are measured using the "Shortest Possible Route" (SPR). The people who certify marathon courses, like those from World Athletics or the USATF, use a Jones Counter on a bicycle. They ride the "tangents." This means they cut every corner as tight as humanly possible.
Unless you are an elite runner with a lead police escort, you aren't running the tangents. You're weaving around people. You're swinging wide at water stations. You're drifting to the side to high-five a kid with a funny sign. Every time you aren't on the perfect line, you're adding meters. Over 42.195 km, those "tiny" deviations add up to a significant distance.
Training for the 42.195 km reality
You don't train for a marathon by running a marathon every day. That’s a one-way ticket to a stress fracture.
Most training plans, whether you're looking at Higdon, Pfitzinger, or Hansons, cap the "Long Run" at about 32 km (20 miles). There’s a law of diminishing returns. Running more than three hours in a single session increases your injury risk exponentially without providing much extra aerobic benefit.
The goal of training is to teach your body to:
- Burn fat more efficiently at higher speeds (glycogen sparing).
- Strengthen your connective tissues so your knees don't explode.
- Build the mental callus required to handle the boredom and the pain.
Elite runners like Eliud Kipchoge or Ruth Chepngetich aren't just faster; they are more efficient. When Kipchoge ran the first sub-two-hour marathon (the INEOS 1:59 Challenge), he was moving at a pace of roughly 2 minutes and 50 seconds per kilometer. For 42 kilometers. To put that in perspective, most fit gym-goers struggle to hold that pace for a single 400-meter lap on a track.
The psychological weight of the final 2.195 km
The "marathon is two races," they say. There's the first 32 km, and then there's the last 10.
That final 2.195 km is often where the real drama happens. In the 1908 Olympics, the leader Dorando Pietri collapsed five times in the final 385 yards. He had to be helped across the line by officials and was eventually disqualified because of it. It’s a brutal stretch of road.
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Mathematically, the 0.195 km is less than 0.5% of the total distance. Mentally, it feels like half the race. This is why people get "26.2" tattoos. It’s a badge of surviving that specific, weird, royal-mandated extra bit.
Actionable steps for your first 42.195 km
If you're planning to tackle the full km in a marathon, stop focusing on the total number and start focusing on the systems.
Respect the taper. Two weeks before the race, cut your mileage. Your body needs to repair the micro-tears in your muscles. You'll feel restless and "fat," but it’s necessary.
Master your fueling. Practice eating gels or chews during your long runs. You need roughly 30 to 60 grams of carbohydrates per hour. If you wait until you're hungry at km 25, it’s already too late. Your gut shuts down when it’s under stress, so you have to train your stomach just like your legs.
Run the tangents. It sounds simple, but look ahead. If the road curves left, get to the left side early. Don't run the outside of a curve unless you want to add an extra 100 meters to your day.
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Forget the watch at the end. In those final few kilometers, your GPS will likely be off due to tall buildings or just the natural weaving of the course. Trust the markers on the road. When you see the sign for "42 km," you have 195 meters of glory left. Sprint it, shuffle it, or crawl it—just don't stop.
The distance is fixed, but how you handle those 42.195 kilometers is entirely up to your training and your head. It’s a long way. It’s supposed to be.