How Many Miles Is A 100K & How to Train For One

So, you’re thinking about running a 100K race?

We’re talking over 62 miles here—no small feat!

Think of it as two marathons back-to-back. It’s a huge distance.  It’s also 49 more miles than a half marathon and the equivalent of running twenty 5Ks in a row.

Calling it a huge challenge is no exaggeration!

But don’t get me wrong.

With the right prep and mindset, running 100K is absolutely within reach.

Let’s break down what’s worked for me and other runners tackling this distance.

So, What Exactly is 100K?

First things first. One kilometer equals 0.621 miles. So if you multiply 0.621 by 100, you get 62.1 miles.

In other words, a 100k race will have you running 62.1 miles.

That’s a lot of miles.

Still not making any sense?

Let me put that number in perspective.

Running a 100k is the equivalent of running 49 miles more than a half marathon, 36 miles more than a marathon, and over 30 miles more than a 50K.

The race is also the equivalent of 20 5K and ten 10K.

Yes, imagine running twenty 5K races in a row.

It’s a lot, isn’t it?

How long does it Take to Run a 100K?

The 100K distance may take most runners around 10 to 15 hours to cross the finish line. It means running through meals, the dark, and spending a full day on your feet.

If you’ve done long distances before, you know it’s as much about pacing and grit as it is about miles.

In my first ultra, somewhere around hour 10, I started asking myself why I was even doing this! But trust me, the feeling of crossing that finish line after such an intense journey is something you won’t forget.

Overall, a good 100k time is 09:09:35. If you’re wondering where I got that number, then know it’s the average 100K time across all ages and genders. A fast 100K time is anything within six hours.

Are You Ready for A 100K?

Before jumping into 100K training, it helps to have some ultra-distance experience.

Increasing your training volume over time will grant your body enough to adapt. Jumping from 5K to 100k is the recipe for failure.

The longer the distance of the race, the more time your body will need to adapt to a higher load. There’s no way around it.

Aim to have at least a few 50-milers under your belt first. When you follow this recipe, you’ll have to add 20k. Yes, by no means a short distance, but it’s better than jumping from a shorter distance.

To ensure you’re making the right decision, it’d best to have completed these 50-mile races feeling pretty good.

Building Your Base

Before you start tackling ultras, make sure you’ve got a solid base.

I recommend focusing on running pain-free for at least 6-12 months before jumping into a race like this. I’ve seen too many runners rush the process and end up injured.

Try to get in five weekly runs, keeping them easy and slowly increasing the mileage

Eventually, you’ll consistently run 18-20 miles for your long runs. Trust me, patience pays off.

Get Your Mind Ready Too

Running 100K is as much mental as it is physical. I’ve had races where the physical pain was less of an issue than the mental hurdles I had to overcome.

You’ll definitely hit some low points along the way. But training your mind to keep going when your body wants to quit is crucial.

I remember hitting mile 40 in my first 100K, and every part of me wanted to quit. My legs felt like lead, and mentally, I was questioning why I’d signed up for this. But what got me through was focusing on small milestones—the next aid station, the next hill, the next mile. Breaking the race into smaller chunks made 62 miles feel less intimidating.

I know this sounds easier said then done, but believe me – once you train your mind as hard as you train your body – you’ll get my point.

Spend Time on Your Feet

More than anything else, you need to get used to spending hours on your feet. Your body has to adapt to spending hours and hours on your feet to withstand the challenge on race day.

When I started upping my long runs, it wasn’t about speed; it was about time. You’ll want to incorporate long, slow runs into your weekly routine, gradually increasing the distance. Hiking is a great way to build endurance without the impact of running.

Aim to complete at least one 50K or longer run a few weeks out in the lead-up to your race. I’m a big fan of back-to-back long runs—this simulates running on tired legs, which is exactly what you’ll face in the later stages of a 100K.

Don’t Skimp on Fueling

In my experience, what and when you eat can make or break your race.

Trust me, while some choices sent me zipping along the trails, others had me wishing for a roadside pickup! You’ll want to find that perfect mix of carbohydrates, sugars, and electrolytes to keep your engine running smoothly over those long miles.

Unlike shorter races where you might wing it on minimal fuel, a 100K demands a solid fueling plan. Begin by figuring out how many calories you burn per hour and how much fluid you lose. This isn’t just guesswork; use a formula to estimate your caloric needs and take a sweat test to gauge your hydration requirements. This information will be the cornerstone of your fueling strategy.

Here’s a starter list of things you might consider packing in your running belt:

• Fruits – Easy to digest and packed with natural sugars.
• Gummies and Energy Gels – Quick, convenient bursts of energy.
• Energy Bars – For a more substantial fuel source.
• Sports Drinks – These and other muscular endurance supplements are essential, not just for hydration but also for their electrolyte content.

Finding the right combination is a bit of trial and error, but it’s worth the effort. What sits well in your stomach? What gives you a noticeable energy boost without causing a crash? Answering these questions through experimentation will guide you to your optimal race day fueling regimen.

Choosing Your First 100K

The right race can make or break your experience. For your first 100K, avoid anything with crazy elevation changes or extreme weather.

I’ve made the mistake of choosing races that were too challenging for my level, and it’s no fun having to drop out halfway because you weren’t prepared for the conditions. A DNF always sucks no matter the reasons.

I recommend choosing a relatively flat, well-supported event course in a comfortable climate and weather.

Leave things like heat, humidity, elevations, and hyenas for when you’re more experienced. That amazing race through the desert or the jungle or whatever will be there next year—and the year after that—no need to jump stages.

I’ve found websites like UltraSignup super helpful for finding races. You can search by location, distance, and difficulty, which is key when looking for something manageable for your first attempt.

Vertical Gain and Race Strategy:

Another factor to consider is the vertical gain of your race. I recommend choosing a course with limited vertical gain for those new to ultra distances. Vertical gain can be deceiving; a route with significant elevation changes will require different pacing and energy management strategies.

Using the ITRA’s kilometer effort conversion, for every 100 meters of elevation gain, it’s akin to running an extra flat kilometer in terms of effort and time. It’s like turning a 100K into a much longer race.

Integrating Vertical Training:

Different terrains can significantly affect your pacing. Running through softer surfaces like mud or sand requires more energy, which can slow you down and extend your total race time.

If your race does involve hills, make sure to include hill workouts in your training. This could be specific hill repeats or incorporating hilly routes into your long runs. Not only does this build strength and endurance, but it also prepares your legs for the descending which can be surprisingly taxing.

Adding these elements into your training helps develop the necessary skills to manage them effectively during the race.

Think about it like this: if you’re running through trails with many loose rocks and roots, practicing on similar trails will help you learn to maintain your speed without tripping or getting injured.

100K Training Plan: Building Endurance and Resilience Step by Step

Training for a 100K race isn’t just about running long distances; it’s about smart, steady progress and recovery. Here’s a breakdown of two tailored 100K training plans: one for beginners who are new to ultras and one for intermediate runners aiming to improve their performance.

Beginner 100K Training Plan

This 24-week plan is designed for those who have a solid running base—meaning you’re comfortable with 20-25 miles per week already. The focus is on gradually building mileage and introducing you to the demands of ultra-distance runs.

Phase 1: Base Building (Weeks 1-8)

• Mileage: Start with around 25 miles per week, increasing by 10% every two weeks.
• Key Workouts:
  • Long Run: Begin with 10 miles, increasing to 16 miles by Week 8.
  • Easy Runs: Two or three runs per week at a relaxed pace.
  • Cross-Training: One session per week (e.g., cycling or swimming).
  • Rest Days: Two days per week to allow recovery and prevent injury.

Phase 2: Building Endurance (Weeks 9-16)

• Mileage: Progress to 30-40 miles per week, with one cutback week every three weeks.
• Key Workouts:
  • Long Run: Build up to 20-22 miles on your longest runs.
  • Back-to-Back Long Runs: Start incorporating back-to-back runs on weekends (e.g., 14 miles on Saturday, 10 on Sunday).
  • Tempo Runs: One weekly run at a comfortably hard pace, about 15-20 minutes.
  • Cross-Training and Core Work: Two sessions a week to strengthen supporting muscles.

Phase 3: Peak Training (Weeks 17-22)

• Mileage: Reach your peak at around 45-50 miles per week.
• Key Workouts:
  • Long Run: Aim for one long run of around 28-30 miles, along with shorter long runs (15-20 miles).
  • Back-to-Back Long Runs: Continue these, ideally aiming for consecutive long efforts on challenging terrain.
  • Intervals: One weekly session of intervals or hill repeats.
  • Cross-Training: Maintain strength and flexibility with yoga, core exercises, or light cycling.

Phase 4: Tapering (Weeks 23-24)

• Reduce mileage to allow your body to recover and prepare.
• Keep up with shorter, easy runs and one last long effort at about half your peak distance.

Intermediate 100K Training Plan

If you’re already running 40+ miles weekly and have experience with marathons or shorter ultra distances, this 20-week plan is for you. It will help you fine-tune your endurance and sharpen your race strategy.

Phase 1: Building Speed and Strength (Weeks 1-6)

• Mileage: Start with 35 miles per week, building up to 45-50.
• Key Workouts:
  • Long Run: Begin with 15 miles, building to 22 miles by Week 6.
  • Speed Work: Incorporate weekly intervals or tempo runs for improved speed.
  • Hill Workouts: Hills build strength—add one hilly run per week or hill repeats.
  • Cross-Training: Focus on core and lower body strength twice weekly.

Phase 2: Building Endurance (Weeks 7-14)

• Mileage: Increase to 55-60 miles per week.
• Key Workouts:
  • Long Run: Work up to 28-30 miles, focusing on back-to-back long weekends.
  • Back-to-Back Runs: Practice two consecutive long days to mimic race fatigue.
  • Tempo Runs and Fartlek: Alternate these weekly to keep variety and build mental toughness.
  • Recovery Runs: Two easy-paced runs weekly to help recover while keeping mileage up.

Phase 3: Peak Training (Weeks 15-18)

• Mileage: Peak at 65-70 miles per week.
• Key Workouts:
  • Ultra Long Run: Try a single long effort of around 35 miles with fueling practice.
  • Race Simulation Runs: Mix in race-specific elements like trail terrain, hills, and planned pacing.
  • Intervals and Hill Repeats: Keep one session each week to maintain strength and agility.
  • Cross-Training: Light strength training to avoid fatigue as you peak.

Phase 4: Tapering (Weeks 19-20)

• Reduce weekly mileage by half, focusing on easy, relaxed runs.
• Aim for one final “longer” effort of about 15 miles but avoid intensity.

Common 100K Training Questions

I know that you have more than one pressing questions when it comes to running a 100K.  Let me address some of the most common concerns.

What should I eat before a 100K run?

Before a 100K ultra marathon, focus on a balanced meal that combines complex carbs, lean protein, and healthy fats to provide sustained energy. Great options include oatmeal with almond butter and fruit, a quinoa bowl with grilled chicken and veggies, or a hearty smoothie with oats, banana, protein powder, and a handful of nuts. Aim to eat 3-4 hours before the race to give your body time to digest, then have a small snack (like a banana or energy bar) about 30-60 minutes before starting.

How many miles should I run each week when training for a 100K?

Weekly mileage for 100K training varies based on experience. For beginners, aim to start around 20-30 miles per week and gradually build up to a peak of 45-50 miles. Intermediate runners might start at 35 miles per week, eventually reaching 60-70 miles in peak weeks. Balance these miles with recovery days to avoid overtraining.

What gear is essential for a 100K ultra marathon?

For a 100K race, the right gear can make a big difference. Essentials include a comfortable hydration vest or pack, trail shoes with good traction, moisture-wicking clothing, and layers if you’re running in varying weather conditions. Don’t forget blister prevention items like anti-chafing balm and high-quality socks. Fuel and hydration options—like gels, electrolyte tablets, and energy bars—are also key for maintaining energy throughout the race.

How much recovery do I need after a 100K run?

After completing a 100K, expect to need at least two to three weeks of dedicated recovery time. Focus on gentle movement, like walking or light stretching, for the first week. Slowly ease back into running with short, easy sessions, and listen to your body to avoid pushing too soon. Hydration, proper nutrition, and plenty of rest will help speed up your recovery process.

What Makes a 100K Different?

Training for a 100K, often referred to as an ultra-marathon, isn’t like training for shorter races. The focus here shifts to building “staying power” through extended runs, back-to-back long efforts, and incorporating variety through endurance run training. Here’s where to start:

• Mileage Progression: Instead of peaking at a marathon’s 26 miles, you’ll want to build to 30-35 miles in one effort, with back-to-back runs becoming part of your routine.
• Fueling Strategy: One of the keys to successful 100K ultra running is developing a fueling plan. At these distances, your body needs steady fuel to maintain energy and avoid hitting the dreaded wall.
• Mental Prep: Let’s not forget the mental side. Preparing for ultra races requires training your mind to stay resilient and adaptable, which is where ultra-endurance training techniques—like visualization and positive self-talk—come in.