🌤️ Running Conditions
Check local weather to get pace adjustments and hydration tips.
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| Distance | Predicted Time | Avg Pace /km |
|---|---|---|
| 5K | 25m 0s | 5:00 |
| 10K | 52m 7s | 5:13 |
| Half Marathon | 1h 55m 0s | 5:27 |
| Marathon | 3h 59m 47s | 5:41 |
| 50K Ultra | 4h 47m 2s | 5:44 |
Riegel formula: T2 = T1 × (D2/D1)^1.06. Assumes equivalent training for each distance.
The formula
T2 = T1 * (D2 / D1) ^ 1.06
Full derivation and the conditions it holds under are in Method and basis, below.
Method and basis
How the figure above is derived, and when not to act on it.
The Standard: Riegel's Formula
This calculator uses Peter Riegel's formula:T2 = T1 * (D2 / D1) ^ 1.06. This assumes you have the appropriate aerobic base for the target distance.⚠️ The "Endurance Gap"
A fast 5K time shows a large engine (VO2 Max), but a Marathon requires Metabolic Efficiency. * The Wall: Your body stores ~2,000 calories of glycogen. A marathon burns ~2,600. Without fueling, you will "hit the wall" at Mile 20 (32km).📈 Metabolic Flexibility & Fueling
To bridge the endurance gap, athletes must train their bodies to oxidize fat at higher intensities. * Carb Loading Protocol: Increase carb intake to 8-10g per kg of bodyweight for 36-48 hours before the race to maximize glycogen stores. * During Race: Aim for 60-90g of carbohydrates per hour.📉 Prediction Accuracy by Weekly Mileage
| Weekly Mileage | Reliability | Impact |
|---|---|---|
| < 30km** | **Poor | Survival mode only. |
| 60-90km** | **High | Prediction is highly accurate. |
| > 100km** | **Extreme | Might beat the prediction. |
🌡️ Environmental Scaling (The Heat Tax)
Temperature is the greatest "un-predictor" of race performance. * Ideal: 45°F - 55°F (7°C - 13°C). * Warm (> 70°F / 21°C): Add 5-15 seconds per kilometer to your goal pace to avoid overheating. * Dew Point: High humidity prevents sweat evaporation, driving core temperature up exponentially.WinSport Editorial & Research Standards
All formulas and reference values used in this tool are sourced from peer-reviewed scientific literature and validated clinical guidelines. Our research team continuously audits each calculator for accuracy and updates methodology as new evidence emerges.
Read the Science
Sports Science Articles- Your 5K Time Doesn't Predict Your Marathon — And Aerobic Decoupling Explains WhyVO2max alone can't predict marathon performance. Aerobic decoupling — the divergence between pace and heart rate over time — is the metric serious marathon runners need to understand.5 min read
- A 3:15 Marathon at 55 Might Be More Impressive Than 2:45 at 28. World Masters Athletics Has the Maths.Age-graded performance factors let masters athletes compare times across age groups using World Masters Athletics tables. Here's the science behind age-adjusted marathon prediction.5 min read
- Your 3:30 Marathon Pace Was Built in October. It's June Now. Here's What Changes.Race performance degrades predictably with temperature. A 3:30 marathoner can expect to lose 10–20 minutes in warm conditions. Here's the physiological mechanism.5 min read
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