Cardiorespiratory Fitness
Running Pace Calculator
Enter one recent race and this calculator predicts your times and per-kilometre pace for the 5K, 10K, half and full marathon, using Riegel's endurance formula (a fatigue factor of 1.06). Marathon predictions read optimistic if your long-run endurance lags your shorter-distance speed, so treat the full as a ceiling, not a promise.
Enter one honest race effort and see your pace per kilometre plus your predicted 5K, 10K, half and full marathon times. It uses Riegel's endurance formula, the same maths behind most race predictors, with the caveats stated plainly rather than hidden.
One race tells you a lot
A single all-out race is a surprisingly good window into your current fitness. Riegel's formula takes that effort and projects how you should run at other distances, because endurance decays at a predictable rate as distance climbs. It is why a strong 10K time is a fair predictor of your half, and why the marathon sits furthest from the prediction: the last 10 km are governed by endurance and fuelling, not the speed your shorter races reveal. Training for a race in Singapore adds heat and humidity on top, which is why the number on this page is a starting reference, not a finish-line promise. If you are chasing a specific time, our personal training for runners builds the strength and durability that turn an optimistic marathon prediction into a realistic one.
How the prediction works
Riegel's endurance model, T2 = T1 times (D2 / D1) raised to the power 1.06. Source: Riegel PS 1981, American Scientist 69(3):285-290.
| Distance | Why it matters for the prediction |
|---|---|
| 5K & 10K | Speed-limited; predict each other well |
| Half marathon | Bridge distance; reliable from a recent 10K |
| Marathon | Endurance-limited; the prediction reads optimistic if long-run fitness lags |
Planning a race this year? See the full Singapore running events calendar and, once you have a target, our guide to the best time to run in Singapore's heat.
Running pace, common questions
- How does the running pace calculator predict my other race times?
- It uses Riegel's endurance formula, T2 = T1 times (D2 divided by D1) to the power of 1.06. The 1.06 is an empirically-derived fatigue factor: for every doubling of distance you slow by a predictable amount. Enter one honest race effort and it projects the rest, from 5K up to the marathon.
- How accurate is a Riegel race-time prediction?
- It is a good ballpark from a recent all-out effort, most reliable for distances close to the one you entered. It assumes equal fitness and even pacing across distances and makes no allowance for heat, humidity, or hills, which all matter in Singapore. The marathon estimate in particular reads optimistic unless your long-run endurance matches your speed, the exact gap structured training closes.
- What is a good pace per kilometre?
- It is personal and depends on distance, age, and training age, so compare yourself against your own past results rather than a universal number. A more useful question is whether your easy runs are genuinely easy and your hard runs genuinely hard. Most recreational runners improve fastest by running most of their weekly volume slower than they think they should.
- Should I use my race pace for every run?
- No. Racing all your runs is the most common way to stall. A sound week is mostly easy aerobic running, often called zone 2, with a small dose of faster work near your target race pace. The pace here is a race-day and threshold reference, not the pace for your daily runs.
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