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Marathon Pace Calculator

Enter any race distance and target time to get your pace per km and mile, a full 5K split schedule, and Riegel-predicted finishing times — all computed in your browser, nothing sent anywhere.

By Karina Zulmery Suárez Bustos , Industrial engineer
Last updated:

What this Marathon Pace Calculator does

This English-language marathon pace calculator gives you three views at once: your exact pace per kilometer and per mile, a 5K split schedule you can write on your wrist or load into a pacing band, and Riegel-predicted equivalent times across 5K, 10K, half marathon, and full marathon. Whether you're planning a goal pace off a recent half marathon or building a marathon pace chart for race day in Chicago, you get all the numbers in one place. The Riegel formula — published in American Scientist in 1981 and adopted by World Athletics — uses a 1.06 fatigue exponent that holds remarkably well for flat-road distances between 3 km and 42 km. 100% client-side — your data never leaves your browser. No uploads, no tracking, no server logs. If you're also tracking calorie burn during training, the [Calories Burned Calculator](/en/calories-burned-calculator/) pairs naturally with your pace work.

Features

  • Pace per km and mile. Converts your target time to pace per kilometer and per mile using the precise 1.609344 km/mi factor — not the rough 1.6 approximation that can add several seconds of error over a marathon.
  • Riegel race-time predictions. Applies Pete Riegel's 1981 formula (T₂ = T₁ × (D₂/D₁)^1.06) to project equivalent finishing times at 5K, 10K, half marathon, and marathon. This is the same model most coaches use when a runner has a recent 10K but is targeting a half marathon.
  • 5K split schedule. Generates a full split table at constant pace — every 5K checkpoint labeled with cumulative time — so you can plan your marathon split calculator wristband or check in at each mile marker without doing mental math mid-race.
  • Speed in km/h and mph. Shows equivalent treadmill speed alongside pace so you can match your road target to a treadmill setting. Note that treadmill belts can run 5–8 sec/km optimistic versus road conditions.
  • Custom distance support. Enter any distance in kilometers — useful for trail races, tune-up efforts at 15K or 25K, or custom time-trial distances your coach prescribes.
  • Half marathon pace chart built in. The predictions table doubles as a half marathon pace chart and half marathon pace converter: input your marathon goal and the tool shows your implied half split, or work backwards from a recent half time to estimate marathon readiness.

How to use the Marathon Pace Calculator

Pick a standard distance or type a custom one, enter your target time, and the results update instantly.

  1. Select your race distance. Choose 5K, 10K, half marathon, or marathon from the dropdown, or type a custom distance in kilometers — for example 16 for a 16 km tempo effort.
  2. Enter your target time. Type the goal time in hh:mm:ss format (e.g. 3:30:00 for a 3:30 marathon) or mm:ss for shorter distances. The calculator accepts both.
  3. Read your pace and speed. Pace per km, pace per mile, km/h, and mph appear immediately. These are your training and race-briefing numbers.
  4. Check equivalent race times. The Riegel predictions table shows what your current fitness implies at other standard distances. Use this to sanity-check whether your marathon goal aligns with your recent 10K result.
  5. Save your split schedule. Screenshot or print the 5K split table. Many runners write key checkpoints on a pacing wristband before a marathon race.

Common use cases

  • Setting a marathon goal from a recent half. If you ran a 1:45 half marathon in San Francisco, enter that time at half-marathon distance and let Riegel project your marathon equivalent. Most coaches treat this as the starting point for a 16-week build.
  • Building a race-day pacing wristband. Print the 5K split schedule and circle your key checkpoints — 10K, 21K, and 30K are the usual decision gates. Constant-pace splits are easier to execute than converting on the fly during a race.
  • Monthly training-block check-ins. Run a 10K time trial every four weeks, plug in the result, and watch the Riegel marathon prediction improve. It's a low-cost way to track fitness without racing a full marathon in training.
  • Coach-athlete communication. Coaches often prescribe pace in min/km while athletes from the U.S. think in min/mile. Enter the target once and share both numbers to eliminate confusion during team briefings.
  • Comparing treadmill workouts to road targets. A 5:00/km treadmill pace is rarely equivalent to 5:00/km outdoors. The speed (km/h) display lets you set the machine correctly, then adjust for the real-world gap during your next outdoor long run. For calorie estimates alongside your training paces, see the [TDEE calculator](/en/tdee-calculator/).

Frequently asked questions

Does the calculator store my times or upload anything?

No. All arithmetic runs locally in your browser using JavaScript. Nothing is sent to a server, logged, or shared. You can disconnect from the internet after the page loads and the tool still works.

How accurate is the Riegel formula for marathon prediction?

For flat-road races between 3 km and 42 km with equivalent training, Riegel is accurate within roughly 1–3% for most trained runners. Accuracy drops for ultras (50K+), hilly courses, or if you're extrapolating from a distance you don't race regularly. A 5K specialist predicting a marathon finish should expect the estimate to be optimistic.

What is the 1.06 fatigue exponent and can I change it?

The exponent captures how pace degrades as distance increases. Riegel derived 1.06 from athletic world records published in 1981; World Athletics and most coaches still use it as the default for road distances. For ultra-distance events (50K and beyond), exponents of 1.07–1.10 tend to fit better. This calculator uses the standard 1.06 for the distances it targets.

Why does my marathon pace chart show different numbers than other calculators?

The most common difference is the km-to-mile conversion factor. Some calculators use 1.6 (off by 0.009344), which compounds over 42.195 km into a 15–20 second error. This tool uses the exact factor 1.609344. Another source of variation is whether the calculator rounds intermediate results — this one carries full floating-point precision through the chain.

Should I aim for even splits or a negative split in a marathon?

Research and race data consistently show that even pace or a slight negative split — running the second half 1–2% faster than the first — produces better finishing times for the vast majority of runners. Positive splits (going out too fast) are the leading cause of the infamous 'wall' after 30 km. Use the 5K split table here to plan an even-pace baseline, then discuss adjustments with your coach.

Can I use this as a half marathon split calculator?

Yes. Select 'half marathon' from the distance dropdown, enter your goal time, and the 5K split schedule covers all checkpoints through 21.0975 km. The Riegel table will also show your implied 5K and 10K paces, which is useful for setting early-race effort cues.