Running Pace Calculator
Use this running pace calculator to calculate your pace, time, or distance and predict your finish time at another race distance.
Calculated instantly in your browser — nothing is sent to or stored on our servers.
Lynn Marie Morski, MD, JD
Lynn-Marie Morski, MD, JD, is a board-certified sports medicine physician who trained at the Mayo Clinic and completed a fellowship at the University of Arizona.
Medical Disclaimer: This calculator provides a general estimate based on established research and is for educational purposes only, not a substitute for medical advice. Individual results can vary based on health conditions, so consult a qualified healthcare professional or registered dietitian before making significant changes to your diet, exercise, or health routine. Read our full Medical Disclaimer.
How Running Pace Is Calculated
This calculator does two different things. Most of the time, you already know two of the three values, pace, time, or distance, and simply need to calculate the third. That’s straightforward math.
But if you've run one race distance and want to know what it predicts for another, a 10K time predicting your marathon, say, that's a different question with real research behind it, not just arithmetic.
What This Calculator Measures
The Pace, Time & Distance mode performs basic running math calculations. The Race Time Predictor mode estimates an equivalent performance at a different distance, using a formula built from real race-time data.
The Formula
Pace, Time & Distance mode uses basic equations:
Pace = Time ÷ Distance
Time = Pace × Distance
Distance = Time ÷ Pace
Race Time Predictor mode uses Riegel's formula, developed by research engineer Pete Riegel from an analysis of world-record running performances ranging from about 1,500 meters to the marathon (26.2 miles)¹.
T2 = T1 × (D2 ÷ D1)^1.06
T1 and D1 are your known time and distance; T2 is the predicted time; and D2 is the target distance. The 1.06 exponent reflects the fact that pace naturally slows as distance increases - which isn't a law of physics, but instead is an empirical pattern calculated with real race results.
How This Calculator Computes Your Result
First, choose what you want to calculate: Pace, Time, or Distance. The calculator shows only the two fields it needs from you and solves for the one you selected, converting between miles and kilometers automatically. In Race Time Predictor mode, select your known race distance and enter your finish time, then choose a target distance, or view predictions across every standard distance at once.
What Your Result Means
Alongside your predicted time, we show a reference table projecting your pace across every standard race distance. For example, a 45:00 10K predicts roughly the following¹:
Distance | Predicted Time |
5K | 21:35 |
10K | 45:00 (user input) |
Half Marathon | 1:39:17 |
Marathon | 3:27:01 |
Why Predictions Get Less Reliable at Longer Distances
Riegel's original exponent was fitted to world-record performances, elite athletes racing under ideal conditions, not recreational runners¹.
A large study surveying 2,303 recreational endurance runners tested how well the formula actually predicts real-world results². It found the formula was well-calibrated for distances up to the half marathon, but it dramatically underestimated marathon finish times, predicting times at least 10 minutes too fast for half of the runners studied.
In practical terms, the shorter your known distance and the longer your target distance, especially when predicting a marathon, the more the formula is likely to underestimate your time..
This isn't unique to Riegel's formula either. A systematic review of marathon prediction methods found over 100 different equations in use across the research literature, none of which were accurate for every runner³.
A Note on Accuracy
Riegel's underlying running data covers efforts from about 3.5 to 129 minutes, elite marathon pace or faster, so most recreational marathon times fall outside that range. Predictions are also most reliable when your known and target distances are close together, a half marathon predicts a marathon far better than a 5K does. This is a population-level model, not a personalized one, and it doesn't account for terrain, weather, race-day pacing, or your specific training.
Frequently Asked Questions
How accurate is a race time prediction?
It depends heavily on the distance gap. Predictions up to the half marathon are reasonably accurate, but predictions of marathon time tend to be underestimated, often by 10 minutes or more².
Why does my predicted marathon time seem too fast?
This is a documented, known limitation of the underlying formula, not a bug. It was originally built from elite world-record data, and a large study of recreational runners found it specifically underestimates marathon finish times². Treat a marathon prediction as an optimistic outcome, not a guarantee.
Can I predict a marathon time from a 5K?
You can, but the further apart your known and target distances are, the less reliable the prediction. A half marathon or 10-mile time will generally predict your marathon time more accurately than a 5K will.
Does this account for hills, weather, or altitude?
No. Both calculation modes are based on your entered pace, time, and distance alone.The Race Time Predictor's formula was built from race results without adjusting for course conditions. Treat results as a flat-course, favorable-conditions estimate.
Sources
Athletic Records and Human Endurance, Riegel, 1981
An Empirical Study of Race Times in Recreational Endurance Runners, Vickers & Vertosick, 2016
Prediction Equations for Marathon Performance: A Systematic Review, Keogh et al., 2019
Running Pace Calculator
Use this running pace calculator to calculate your pace, time, or distance and predict your finish time at another race distance.
Calculated instantly in your browser — nothing is sent to or stored on our servers.
Lynn Marie Morski, MD, JD
Lynn-Marie Morski, MD, JD, is a board-certified sports medicine physician who trained at the Mayo Clinic and completed a fellowship at the University of Arizona.
Medical Disclaimer: This calculator provides a general estimate based on established research and is for educational purposes only, not a substitute for medical advice. Individual results can vary based on health conditions, so consult a qualified healthcare professional or registered dietitian before making significant changes to your diet, exercise, or health routine. Read our full Medical Disclaimer.
How Running Pace Is Calculated
This calculator does two different things. Most of the time, you already know two of the three values, pace, time, or distance, and simply need to calculate the third. That’s straightforward math.
But if you've run one race distance and want to know what it predicts for another, a 10K time predicting your marathon, say, that's a different question with real research behind it, not just arithmetic.
What This Calculator Measures
The Pace, Time & Distance mode performs basic running math calculations. The Race Time Predictor mode estimates an equivalent performance at a different distance, using a formula built from real race-time data.
The Formula
Pace, Time & Distance mode uses basic equations:
Pace = Time ÷ Distance
Time = Pace × Distance
Distance = Time ÷ Pace
Race Time Predictor mode uses Riegel's formula, developed by research engineer Pete Riegel from an analysis of world-record running performances ranging from about 1,500 meters to the marathon (26.2 miles)¹.
T2 = T1 × (D2 ÷ D1)^1.06
T1 and D1 are your known time and distance; T2 is the predicted time; and D2 is the target distance. The 1.06 exponent reflects the fact that pace naturally slows as distance increases - which isn't a law of physics, but instead is an empirical pattern calculated with real race results.
How This Calculator Computes Your Result
First, choose what you want to calculate: Pace, Time, or Distance. The calculator shows only the two fields it needs from you and solves for the one you selected, converting between miles and kilometers automatically. In Race Time Predictor mode, select your known race distance and enter your finish time, then choose a target distance, or view predictions across every standard distance at once.
What Your Result Means
Alongside your predicted time, we show a reference table projecting your pace across every standard race distance. For example, a 45:00 10K predicts roughly the following¹:
Distance | Predicted Time |
5K | 21:35 |
10K | 45:00 (user input) |
Half Marathon | 1:39:17 |
Marathon | 3:27:01 |
Why Predictions Get Less Reliable at Longer Distances
Riegel's original exponent was fitted to world-record performances, elite athletes racing under ideal conditions, not recreational runners¹.
A large study surveying 2,303 recreational endurance runners tested how well the formula actually predicts real-world results². It found the formula was well-calibrated for distances up to the half marathon, but it dramatically underestimated marathon finish times, predicting times at least 10 minutes too fast for half of the runners studied.
In practical terms, the shorter your known distance and the longer your target distance, especially when predicting a marathon, the more the formula is likely to underestimate your time..
This isn't unique to Riegel's formula either. A systematic review of marathon prediction methods found over 100 different equations in use across the research literature, none of which were accurate for every runner³.
A Note on Accuracy
Riegel's underlying running data covers efforts from about 3.5 to 129 minutes, elite marathon pace or faster, so most recreational marathon times fall outside that range. Predictions are also most reliable when your known and target distances are close together, a half marathon predicts a marathon far better than a 5K does. This is a population-level model, not a personalized one, and it doesn't account for terrain, weather, race-day pacing, or your specific training.
Frequently Asked Questions
How accurate is a race time prediction?
It depends heavily on the distance gap. Predictions up to the half marathon are reasonably accurate, but predictions of marathon time tend to be underestimated, often by 10 minutes or more².
Why does my predicted marathon time seem too fast?
This is a documented, known limitation of the underlying formula, not a bug. It was originally built from elite world-record data, and a large study of recreational runners found it specifically underestimates marathon finish times². Treat a marathon prediction as an optimistic outcome, not a guarantee.
Can I predict a marathon time from a 5K?
You can, but the further apart your known and target distances are, the less reliable the prediction. A half marathon or 10-mile time will generally predict your marathon time more accurately than a 5K will.
Does this account for hills, weather, or altitude?
No. Both calculation modes are based on your entered pace, time, and distance alone.The Race Time Predictor's formula was built from race results without adjusting for course conditions. Treat results as a flat-course, favorable-conditions estimate.
Sources
Athletic Records and Human Endurance, Riegel, 1981
An Empirical Study of Race Times in Recreational Endurance Runners, Vickers & Vertosick, 2016
Prediction Equations for Marathon Performance: A Systematic Review, Keogh et al., 2019
Running Pace Calculator
Use this running pace calculator to calculate your pace, time, or distance and predict your finish time at another race distance.
Calculated instantly in your browser — nothing is sent to or stored on our servers.
Lynn Marie Morski, MD, JD
Lynn-Marie Morski, MD, JD, is a board-certified sports medicine physician who trained at the Mayo Clinic and completed a fellowship at the University of Arizona.
Medical Disclaimer: This calculator provides a general estimate based on established research and is for educational purposes only, not a substitute for medical advice. Individual results can vary based on health conditions, so consult a qualified healthcare professional or registered dietitian before making significant changes to your diet, exercise, or health routine. Read our full Medical Disclaimer.
How Running Pace Is Calculated
This calculator does two different things. Most of the time, you already know two of the three values, pace, time, or distance, and simply need to calculate the third. That’s straightforward math.
But if you've run one race distance and want to know what it predicts for another, a 10K time predicting your marathon, say, that's a different question with real research behind it, not just arithmetic.
What This Calculator Measures
The Pace, Time & Distance mode performs basic running math calculations. The Race Time Predictor mode estimates an equivalent performance at a different distance, using a formula built from real race-time data.
The Formula
Pace, Time & Distance mode uses basic equations:
Pace = Time ÷ Distance
Time = Pace × Distance
Distance = Time ÷ Pace
Race Time Predictor mode uses Riegel's formula, developed by research engineer Pete Riegel from an analysis of world-record running performances ranging from about 1,500 meters to the marathon (26.2 miles)¹.
T2 = T1 × (D2 ÷ D1)^1.06
T1 and D1 are your known time and distance; T2 is the predicted time; and D2 is the target distance. The 1.06 exponent reflects the fact that pace naturally slows as distance increases - which isn't a law of physics, but instead is an empirical pattern calculated with real race results.
How This Calculator Computes Your Result
First, choose what you want to calculate: Pace, Time, or Distance. The calculator shows only the two fields it needs from you and solves for the one you selected, converting between miles and kilometers automatically. In Race Time Predictor mode, select your known race distance and enter your finish time, then choose a target distance, or view predictions across every standard distance at once.
What Your Result Means
Alongside your predicted time, we show a reference table projecting your pace across every standard race distance. For example, a 45:00 10K predicts roughly the following¹:
Distance | Predicted Time |
5K | 21:35 |
10K | 45:00 (user input) |
Half Marathon | 1:39:17 |
Marathon | 3:27:01 |
Why Predictions Get Less Reliable at Longer Distances
Riegel's original exponent was fitted to world-record performances, elite athletes racing under ideal conditions, not recreational runners¹.
A large study surveying 2,303 recreational endurance runners tested how well the formula actually predicts real-world results². It found the formula was well-calibrated for distances up to the half marathon, but it dramatically underestimated marathon finish times, predicting times at least 10 minutes too fast for half of the runners studied.
In practical terms, the shorter your known distance and the longer your target distance, especially when predicting a marathon, the more the formula is likely to underestimate your time..
This isn't unique to Riegel's formula either. A systematic review of marathon prediction methods found over 100 different equations in use across the research literature, none of which were accurate for every runner³.
A Note on Accuracy
Riegel's underlying running data covers efforts from about 3.5 to 129 minutes, elite marathon pace or faster, so most recreational marathon times fall outside that range. Predictions are also most reliable when your known and target distances are close together, a half marathon predicts a marathon far better than a 5K does. This is a population-level model, not a personalized one, and it doesn't account for terrain, weather, race-day pacing, or your specific training.
Frequently Asked Questions
How accurate is a race time prediction?
It depends heavily on the distance gap. Predictions up to the half marathon are reasonably accurate, but predictions of marathon time tend to be underestimated, often by 10 minutes or more².
Why does my predicted marathon time seem too fast?
This is a documented, known limitation of the underlying formula, not a bug. It was originally built from elite world-record data, and a large study of recreational runners found it specifically underestimates marathon finish times². Treat a marathon prediction as an optimistic outcome, not a guarantee.
Can I predict a marathon time from a 5K?
You can, but the further apart your known and target distances are, the less reliable the prediction. A half marathon or 10-mile time will generally predict your marathon time more accurately than a 5K will.
Does this account for hills, weather, or altitude?
No. Both calculation modes are based on your entered pace, time, and distance alone.The Race Time Predictor's formula was built from race results without adjusting for course conditions. Treat results as a flat-course, favorable-conditions estimate.
Sources
Athletic Records and Human Endurance, Riegel, 1981
An Empirical Study of Race Times in Recreational Endurance Runners, Vickers & Vertosick, 2016
Prediction Equations for Marathon Performance: A Systematic Review, Keogh et al., 2019