Running Pace Calculator
Calculate pace, predict finish times, and forecast race results using the Riegel formula.
Calculate Your Pace
Enter your distance and finish time to get your pace.
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How to Use the Pace Calculator
- Open the Pace tab. Enter the distance you ran and your total finish time (hours, minutes, seconds). The calculator instantly shows your pace in both min/km and min/mile.
- Open the Finish Time tab. Select a race distance from the dropdown (5K, 10K, Half Marathon, Marathon, and more) or enter a custom distance in kilometers. Type your target pace and choose whether it is per kilometer or per mile. Your projected finish time appears immediately.
- Open the Race Predictor tab. Select your known race distance, enter the time you ran it, and the calculator outputs predicted finish times for all other common race distances using the Riegel formula.
- All three tabs update in real time — no button to press. Change any input and results refresh automatically.
- Pace is shown in both min/km and min/mile regardless of which unit you enter, so you never need to convert manually.
How Pace and Finish Time Are Calculated
Running pace is the time it takes to cover one unit of distance — one kilometer or one mile. The formula is straightforward:
Pace = Total Time ÷ Distance
For example, if you ran 10 km in 55 minutes and 0 seconds (3,300 seconds total), your pace per kilometer is 3,300 ÷ 10 = 330 seconds, which equals 5 minutes and 30 seconds per km (5:30/km). To convert that to a per-mile pace, the calculator multiplies the per-km seconds by 1.60934 (the number of kilometers in one mile): 330 × 1.60934 ≈ 531 seconds, or 8 minutes 51 seconds per mile (8:51/mi).
Going the other direction, Finish Time = Pace × Distance. If your target pace is 6:00 per km and your race is 21.0975 km (a half marathon), the projected finish time is 6 × 21.0975 = 126.585 minutes, or roughly 2 hours, 6 minutes, and 35 seconds.
If you enter a pace in min/mile, the calculator converts it to a per-km pace internally (dividing by 1.60934) before multiplying by the distance in kilometers. This keeps all the math consistent regardless of which unit you prefer to train in.
A Worked Example
Suppose you ran a 10 km race in exactly 50 minutes (50:00). Here is how the numbers work out:
Total time in seconds: 50 × 60 = 3,000 seconds. Divide by 10 km: 3,000 ÷ 10 = 300 seconds per km = 5:00 per km. To get the mile pace: 300 × 1.60934 ≈ 483 seconds = 8:03 per mile.
Now use that pace to estimate finish times at other distances:
| Race | Distance | Finish Time at 5:00/km |
|---|---|---|
| 1 Mile | 1.609 km | 8:03 |
| 5K | 5 km | 25:00 |
| 10K | 10 km | 50:00 |
| Half Marathon | 21.097 km | 1:45:29 |
| Marathon | 42.195 km | 3:29:58 |
Keep in mind these are even-pace projections — they assume you hold exactly 5:00/km for the entire race. In practice, fatigue sets in over longer distances, which is exactly what the Riegel formula accounts for in the Race Predictor tab.
Predicting Race Times (Riegel Formula)
The Race Predictor uses the Riegel formula, published by Pete Riegel in a 1977 paper in Runner's World. It accounts for the fact that performance degrades slightly as distance increases — no one can hold their 5K pace through a marathon.
T2 = T1 × (D2 ÷ D1)^1.06
Where T1 is your known finish time, D1 is the known distance, D2 is the target distance, and T2 is the predicted finish time. The exponent 1.06 is an empirically derived fatigue factor — slightly above 1.0 to reflect the nonlinear relationship between distance and performance.
Example: You ran a 10K in 50:00 (3,000 seconds). Predict your half marathon (21.0975 km): T2 = 3,000 × (21.0975 ÷ 10)^1.06 = 3,000 × (2.10975)^1.06 ≈ 3,000 × 2.227 ≈ 6,681 seconds = 1:51:21. Notice this is longer than the simple even-pace projection of 1:45:29 — the formula builds in the realistic slowdown over the extra distance.
The Riegel formula is most reliable when predicting between distances of similar magnitude (5K to 10K, 10K to half marathon). Accuracy drops for large jumps — for example, using a 1-mile time to predict a marathon — because training specificity, nutrition strategy, and long-run endurance become dominant factors the formula cannot model. Use predictions as a training target, not a race-day guarantee.
The table below shows the equivalent predicted paces for common race distances if your 10K time is 50:00, to illustrate how the Riegel formula adjusts pace expectations at each distance:
| Race Distance | Predicted Finish | Implied Pace (per km) |
|---|---|---|
| 5K | 23:52 | 4:46/km |
| 10K (known) | 50:00 | 5:00/km |
| Half Marathon | 1:51:21 | 5:17/km |
| Marathon | 3:54:04 | 5:33/km |
Frequently Asked Questions
How is running pace calculated?
Pace is calculated by dividing your total time (in seconds) by the distance you covered. The result is seconds per kilometer or seconds per mile, which is then formatted as minutes:seconds. For example, 3,300 seconds over 10 km = 330 seconds/km = 5:30 per km.
What's a good running pace?
“Good” is relative to your experience and goals. A comfortable beginner pace is around 7:00–9:00 per km (11:00–14:30 per mile). Recreational runners often settle around 5:00–7:00 per km (8:00–11:00 per mile). Advanced runners typically train between 4:00 and 5:30 per km (6:30–9:00 per mile). Elite athletes race well under 3:00 per km. The best benchmark is your own progress over time.
How accurate is the race predictor?
The Riegel formula is well-validated for predictions within a two-to-three times distance ratio — such as 5K to 10K or 10K to half marathon. For larger jumps, like a 5K to a marathon, accuracy decreases significantly because endurance training, nutrition, pacing strategy, and aerobic base all become more important than the formula can account for. Always combine the prediction with sport-specific training.
What is the difference between pace and speed?
Speed is distance divided by time (e.g., 12 km/h), while pace is time divided by distance (e.g., 5:00 per km). Runners typically use pace because it directly tells you how long each kilometer or mile will take — which is more useful for pacing a race than a speed number. Cyclists and swimmers more often use speed. To convert: speed (km/h) = 60 ÷ pace (min/km).
How do I convert min/km to min/mile?
Multiply your per-km pace in seconds by 1.60934. For example, 5:00/km = 300 seconds × 1.60934 ≈ 483 seconds = 8:03 per mile. To go the other direction, divide your per-mile seconds by 1.60934. This calculator does both conversions automatically every time you enter a result.
How should my race pace differ from my training pace?
Most training should be done at an easy pace — roughly 60–90 seconds per km slower than your goal race pace. This builds aerobic capacity without excessive fatigue. Only a small portion of weekly mileage (typically 10–20%) should be at race pace or faster. Running all your training at race pace increases injury risk and limits long-term development. Use this calculator to set easy-day targets and distinguish them from your goal race pace.
Can I use a 5K time to predict a marathon?
Technically yes, but the prediction will likely be optimistic. The Riegel formula assumes you have trained appropriately for the target distance. A runner who has only ever raced 5Ks probably lacks the marathon-specific endurance and fueling experience to hit the predicted time. Use a 5K-to-marathon prediction as a distant ceiling, not a race-day target, until you have completed a half marathon under similar conditions.
Pace and finish time calculations use direct division. Race predictions use the Riegel formula (T2 = T1 × (D2/D1)^1.06) and are estimates only. Results are for informational purposes and should not replace advice from a qualified running coach or sports medicine professional.