How many miles is a half marathon? A coach's guide to the 13.1.

The short answer, and why it matters

A half marathon is 13.1 miles, or 21.0975 kilometers to be exact. Officially, the International Association of Athletics Federations sets the distance at 21.0975 km, which rounds to 13.109 miles. Every certified half marathon on the planet, from a small-town road race to the Great North Run, measures the same distance.

Thirteen point one miles takes most runners between 1:30 and 2:30 to finish. That range is wide because the half sits at a specific place in the aerobic ladder. It is long enough that fueling starts to matter, long enough that pacing decisions in the first two miles echo at mile eleven, and short enough that a well-trained runner can hold something close to threshold pace the entire way. That is the whole game.

People search "how many miles is a half marathon" for two reasons. The first is they want a number to plug into a plan. The second is they want to know whether the distance is a big deal. It is. Not because 13.1 is intrinsically far, but because of what it demands physiologically to run it well.

Why 13.1 miles is a specific test, not just "half of a marathon"

The name is misleading. A half marathon is not run at half the intensity of a marathon. It is run considerably faster, at roughly the pace a fit runner can hold for 60 to 100 minutes without falling off. In physiology terms, that is very close to your lactate threshold, the pace where your body is producing lactate right at the edge of what it can clear.

A marathon lives about 20 to 30 seconds per mile slower than that. So the training for a half looks different. You still need aerobic volume, but the workouts sharpen threshold rather than steady endurance. Your longest runs matter less than your threshold work. Your fueling window is shorter and your pacing tolerance is smaller.

The other thing about 13.1: it is long enough to run out of glycogen if you started too fast. Most runners have 90 to 120 minutes of stored carbohydrate at half-marathon effort. If you start at 5K pace and the tank empties at mile 9, the last four miles turn into a walk. This is why half-marathon pacing is a coaching topic, not a stopwatch topic.

The base you actually need before you sign up

The honest floor for training for a half marathon is consistent running three to four times a week for at least eight weeks before you start a focused plan. That gets you to roughly 15 to 20 miles per week of easy aerobic volume. Below that, a 12-week plan compresses too much load into too little runway and the injury math gets ugly.

Here is a rough guide to the base I look for before writing a half marathon plan for someone:

The biggest mistake I see across athletes I coach: signing up for a race 10 weeks out with a 6-mile long run and hoping enthusiasm covers the gap. Enthusiasm does not build capillary density. If your base is short, move the race, not the training. A well-run half at 16 weeks of prep beats a survival march at 10 weeks every time.

How many weeks it actually takes

For a first-time half marathoner with a small base, plan on 16 weeks. For a runner who has done one before and is fit, 10 to 12 weeks works fine. The shape of the block matters more than the length. The three phases:

The number that surprises new half marathoners: your long run does not need to touch 13.1. A long run of 10 to 12 miles is enough for most first-timers. Race-day adrenaline plus a fresh taper covers the last mile and change. What actually predicts a strong race is how easy your easy days were, not whether you ran 13 in training.

The paces that build a strong 13.1

Every half-marathon plan I write pulls from four pace zones. Two build the engine, one sharpens the top, one is the race itself. The paces come from a recent race time run through the VDOT system, not from an internet chart that does not know your fitness.

The workout most first-time half marathoners are missing: threshold intervals at goal half-marathon pace. Two formats I use often. First, 3 to 5 repeats of one mile at goal half pace with 60 to 90 seconds jog rest. Second, 2 to 3 repeats of 2 miles at goal pace plus 10 seconds per mile with two minutes rest. Either format teaches your legs the exact tempo of race day so mile four does not feel like a surprise.

The workout that is overrated for the half: long, slow marathon-pace runs longer than 12 miles. Useful once or twice. Not the workhorse. Save your long-run recovery for the threshold work that actually moves the needle.

Race day: how to pace 13.1 without blowing up

In 15 years of coaching, if I had to name the single biggest reason otherwise fit runners have a bad half marathon, it is starting the first mile 15 to 20 seconds per mile faster than goal pace. It feels fine. The adrenaline covers it. The bill arrives around mile 9.

The rule I give athletes on race morning: the first two miles should feel almost slow. If you are five seconds per mile under goal pace at the two-mile mark, you are exactly where you want to be. From miles three through nine, settle into goal pace. From ten to twelve, hold. Mile thirteen, whatever is left.

Fueling: for anything under about 1:45, a lot of runners can race the half on nothing beyond a good breakfast and water. Above 1:45, one gel around mile 4 and a second around mile 8 catches the glycogen dip before you feel it. Practice both in training. Nothing new on race day, especially at 90 minutes of sustained effort.

Weather: for every 10 degrees above 55 Fahrenheit at the start, add roughly 5 to 10 seconds per mile to goal pace. This is not a suggestion. It is the difference between a race and a bonk.

Four patterns I watch for across half marathoners

These come from patterns I see repeatedly, not from any single athlete:

1. The long-run addict. Runs 12 miles every Sunday and calls it half training. Never does threshold work. Finishes the race under-prepared for pace. The half is a threshold event. Train it like one.
2. The 5K carryover. Fast at 5K, decides 13.1 will feel similar. Starts at 5K pace. Blows up at mile 8. Half pace is a different zone with a different economy. Respect it.
3. The uneven weekly runner. Runs 4 miles Monday, skips Tuesday, does 10 miles Wednesday, skips three days, does another long run. Injury within eight weeks, almost every time. Volume distribution matters as much as total volume.
4. The taper skeptic. Trains hard right up to race week because rest feels like losing fitness. Shows up flat. A proper two-week taper does not cost fitness. It reveals fitness that fatigue was hiding.

The runners who race a half well tend to share three habits: they run six days a week at honest easy paces, they hit their threshold workout weekly, and they treat mile one like it is a warmup they are still finishing. That is most of the recipe.

What to do tomorrow

If you are trying to decide whether you are ready to sign up for a half marathon, or trying to figure out where to start, here is the shortest honest checklist:

1. Count your current weekly mileage across the last four weeks. Not one big week. The average.
2. Look at your longest run in the last month. If it is under 6 miles, add four weeks of base before you start a plan.
3. Take a recent 5K or 10K time and run it through a VDOT calculator to get your true half-marathon goal pace. Not a guess.
4. Pick a race that is at least 12 weeks out if you are experienced, 16 to 20 weeks out if this is your first.
5. Book the strength work and the sleep before you book the mileage. Both matter more than one extra mid-week run.

The distance is 13.1 miles. What makes it worth training for is not the number. It is the fact that a half marathon, done properly, will tell you the truth about how well you have trained. If you want to see how the week-to-week coaching relationship shapes that training, or what the two coaching tiers include, we can talk on a call. Otherwise, keep the easy days easy, put the threshold work in, and race the pace you earned.

Written by

Coach Johnny Crain

2:12 marathoner. 4× US Olympic Marathon Trials qualifier. 4× NCAA national champion and 4× NCAA runner-up. Spoke at the RRCA National Convention. Founder and head coach at RunFitCoach, where he coaches every athlete personally.