Running Pace Calculator
Work out running pace, finish time, or distance from the other two, in km or miles, with splits, negative splits, and Riegel race-time predictions.
Processed locally in your browser — nothing is uploaded.
Running Pace Calculator
h:mm:ss or mm:ss — 1h 45m works too.
Results
- Pace
- 5:00 /km · 8:03 /mi
- Finish time
- 25:00
- Distance
- 5 km · 3.11 mi
- Speed
- 12 km/h · 7.46 mph
Splits
How much faster the second half is. 0 runs it evenly.
| Kilometer | Split | Pace | Elapsed |
|---|---|---|---|
| 1 | 5:00 | 5:00 /km | 5:00 |
| 2 | 5:00 | 5:00 /km | 10:00 |
| 3 | 5:00 | 5:00 /km | 15:00 |
| 4 | 5:00 | 5:00 /km | 20:00 |
| 5 | 5:00 | 5:00 /km | 25:00 |
Predicted times at other distances
| Race | Time | Pace /km | Pace /mi |
|---|---|---|---|
| 1 mile | 7:31 | 4:40 | 7:31 |
| 5K(your race) | 25:00 | 5:00 | 8:03 |
| 10K | 52:07 | 5:13 | 8:23 |
| 15K | 1:20:07 | 5:20 | 8:36 |
| 10 miles | 1:26:19 | 5:22 | 8:38 |
| Half marathon | 1:55:00 | 5:27 | 8:46 |
| Marathon | 3:59:47 | 5:41 | 9:09 |
Estimates from Riegel’s formula (T₂ = T₁ × (D₂ ÷ D₁)^1.06). They assume you’re equally trained for each distance — predictions from a short race usually flatter the marathon, and races much shorter than 1 mile or longer than a marathon fall outside what the formula was fitted to.
About Running Pace Calculator
Pace, finish time, and distance are tied together: know any two and the third follows. Choose what to calculate, pick a race (1 mile, 5K, 10K, 15K, 10 miles, half marathon, marathon) or type a custom distance in kilometers or miles, and enter the other value. The calculator shows pace per kilometer and per mile side by side, the finish time, the distance in both units, and your speed in km/h and mph — useful for setting a treadmill.
Times can be typed as 25:00, 1:45:30, or 1h 45m; a pace like 5:30 means five minutes thirty seconds per kilometer or mile.
Splits
Below the result is a split table — the time for each kilometer or mile, the pace for that split, and the elapsed time at each marker — so you can write target splits on your wrist or program a watch. Race distances rarely end on a whole unit, so the last row is the leftover 0.0975 km of a half marathon or 0.2 miles of a marathon, at the same pace.
Set a negative split to plan a second half that's faster than the first. At 2%, a 3:30 marathon becomes a first half of about 1:46:04 and a second half of about 1:43:56: the same finish time, with the effort saved for later. A split that straddles the halfway point gets a blend of the two paces.
Race predictions
The prediction table uses Peter Riegel's formula, published in 1981 and still the most common race-time predictor: T₂ = T₁ × (D₂ ÷ D₁)^1.06. The exponent says how much a runner slows as the distance grows — 1.06 was Riegel's average fit. If you tend to fade in long races, raise it to 1.08 or 1.10 in Options; if endurance is your strength, lower it.
Example
Input
Half marathon in 1:45:00
Output
Pace 4:59 /km · 8:01 /mi Speed 12.06 km/h · 7.49 mph Predicted marathon (Riegel 1.06): 3:38:55
The prediction assumes marathon-specific training. Many runners finish slower than a half-marathon time predicts, so a conservative first marathon goal sits a few minutes behind it.
Common uses
- Find the pace you need to hold for a goal time, like a sub-2-hour half marathon (5:41 per km, 9:09 per mile)
- Convert a pace per kilometer into a pace per mile, or into a treadmill speed
- Plan even or negative splits for race day
- Estimate a realistic 10K or marathon target from a recent race
Limitations
- Splits assume a flat course and steady effort. Hills, wind, heat, and crowded starts all cost time that the table doesn't know about.
- Race distances are the official lengths. GPS watches usually measure a little long because runners don't follow the exact racing line, so your watch pace will read slightly faster than the official pace.
- Riegel predictions are estimates. They work best between about 1 mile and the marathon, for runners trained for both distances.
Frequently asked questions
How do I calculate my running pace?
Divide your time by the distance. A 5K in 25:00 is 25 minutes ÷ 5 km = 5:00 per kilometer, or 8:03 per mile. A half marathon (21.0975 km) in 1:45:00 works out to about 4:59 per kilometer.
What pace do I need for a sub-2-hour half marathon?
About 5:41 per kilometer or 9:09 per mile. Running exactly 5:41/km gives 1:59:54, so there is only a few seconds of margin — many runners aim for 5:35–5:38/km to allow for weaving and a GPS that measures long.
What pace is a 4-hour marathon?
5:41 per kilometer or 9:09 per mile. Notice it's the same pace as a 2-hour half marathon — the marathon is exactly twice as long. For a 3:30 marathon you need 4:59/km (8:01/mi); for sub-3, 4:15/km (6:51/mi) or faster.
How do I convert pace per kilometer to pace per mile?
Multiply the pace by 1.609 (a mile is 1.609 km). 5:00 per kilometer is 300 seconds × 1.609 = 483 seconds, or 8:03 per mile. To go the other way, divide by 1.609.
What is a negative split?
Running the second half of a race faster than the first. Most distance-running records are set with even or slightly negative splits, because starting conservatively saves glycogen and avoids the lactate build-up that comes from going out too fast. Enter a percentage and the split table spreads it across the race while keeping your finish time.
How accurate is the Riegel race time predictor?
It's a good first estimate between the mile and the half marathon, typically within a few percent for trained runners. It tends to be optimistic for the marathon, especially when predicting from a 5K or for runners without long training runs. Raising the exponent from 1.06 to around 1.08 gives a more cautious marathon prediction.
How do I convert pace to speed for a treadmill?
Divide 60 by your pace in minutes. A 6:00 per kilometer pace is 60 ÷ 6 = 10 km/h; an 8:00 per mile pace is 7.5 mph. The calculator shows both speeds for whatever pace you enter.
Is anything I enter saved or sent?
No. All the math runs in your browser and nothing is uploaded or stored.