Running Pace & Race Finish Time Predictor
Calculate min/mile and min/km running pace, split times, and Pete Riegel race finish predictions from 5K to Marathon.
Riegel Formula Race Predictions
Calculated using the Pete Riegel fatigue exponent (T2 = T1 × [D2 / D1]1.06), assuming comparable aerobic fitness and endurance preparation.
| Race Distance | Predicted Time | Required Mile Pace | Required KM Pace |
|---|
Suggested Workout Training Paces
About this tool
How to use it
- Select your baseline race distance (5K, 10K, 10 Miles, Half Marathon, or Marathon).
- Enter your recorded finish time in hours, minutes, and seconds.
- Instantly view your average running pace in minutes per mile, minutes per kilometer, and miles per hour.
- Review the Riegel Formula race predictions table and suggested workout pace zones (Easy, Tempo, Intervals).
Why it matters
Pacing mistakes in running are unforgiving: starting just 15 seconds per mile too fast in a marathon leads to severe glycogen depletion and 'hitting the wall' at mile 20. Calculating precise splits and realistic predictions based on proven fatigue formulas ensures sustainable race execution.
When to use it
Use this pace calculator when authoring running training blocks, setting GPS watch pace alerts, targeting marathon PRs, or converting treadmill km/h speeds to outdoor mile splits.
Good to know
The Pete Riegel formula (T2 = T1 × [D2/D1]^1.06) was published in Runner's World in 1977 and remains the gold standard for predicting endurance race times from 1,500m up to 100K ultra-marathons.
Common questions
What pace is required for a sub-20 minute 5K?
A sub-20 minute 5K requires an average pace of 6:26 per mile (3:59 per kilometer) or an average speed of 9.32 mph (15.0 km/h).
How accurate is the Pete Riegel race prediction formula?
The Riegel formula has an accuracy of ±2% assuming the runner has completed adequate weekly mileage and endurance long runs appropriate for the target distance.
What pace do I need to break 4 hours in a marathon?
Breaking 4 hours in a full marathon requires an average pace of 9:09 per mile (5:41 per kilometer), finishing at 3:59:59.
What is the difference between tempo pace and easy pace?
Easy pace is run at comfortable Zone 2 conversational effort (typically 90 to 120 seconds slower than 5K pace). Tempo pace is 'comfortably hard' at your lactate threshold (roughly 25 to 30 seconds slower than 5K pace).