Pace, speed, distance and time are one equation
Every running number comes down to three quantities: how far you went, how long it took, and therefore how fast you were. Know any two and the third is fixed. This calculator simply solves that relationship in whichever direction you need.
- Pace per km (seconds) = total time (seconds) ÷ distance (km)
- Average speed (km/h) = 3,600 ÷ pace per km (seconds) = distance (km) ÷ time (hours)
- Total time = distance × pace per km, and distance = total time ÷ pace per km
- Pace per mile = pace per km × 1.609344, because one mile is 1.609344 km
Pace behaves in the opposite direction to speed: a smaller number means faster. A 5:00/km pace is 12.0 km/h and 6:00/km is 10.0 km/h. That looks like a 20 percent gap in speed, but over 10 km it is a ten-minute gap on the clock. Paces should also be combined through time, never by averaging speeds. If you run the first 5 km at 5:00 and the next 5 km at 6:00, the 10 km average pace is 5:30. Averaging 12 and 10 km/h to get 11 km/h is wrong, because you spend more time at the slower speed; the true average speed is about 10.9 km/h.
Worked examples, checked by calculation
Example 1: pace from distance and time. A 10 km run in 50:00 is 3,000 seconds ÷ 10 = 300 seconds per km, which is 5:00/km. The average speed is 12.0 km/h and the mile pace is 300 × 1.609344 = 482.8 seconds, about 8:03 per mile. A 400 m lap takes 300 × 0.4 = 120 seconds, or 2:00.
Example 2: finish time from a target pace. A half marathon (21.0975 km) at 5:30/km (330 seconds) takes 330 × 21.0975 = 6,962 seconds, which is about 1:56:02. The same pace over 42.195 km gives 330 × 42.195 = 13,924 seconds, about 3:52:04.
Example 3: distance from time and pace. Running 45 minutes at 6:00/km covers 2,700 seconds ÷ 360 seconds = 7.5 km.
Pace, speed and race times at a glance
The table assumes a perfectly even pace from start to finish and is calculated at build time. You can also read it backwards: find your goal time in a distance column and look left for the pace you would need.
| Pace /km | Pace /mile | km/h | 5K | 10K | Half | Marathon |
|---|---|---|---|---|---|---|
| 4:00 | 6:26 | 15.0 | 20:00 | 40:00 | 1:24:23 | 2:48:47 |
| 4:30 | 7:15 | 13.3 | 22:30 | 45:00 | 1:34:56 | 3:09:53 |
| 5:00 | 8:03 | 12.0 | 25:00 | 50:00 | 1:45:29 | 3:30:59 |
| 5:30 | 8:51 | 10.9 | 27:30 | 55:00 | 1:56:02 | 3:52:04 |
| 6:00 | 9:39 | 10.0 | 30:00 | 1:00:00 | 2:06:35 | 4:13:10 |
| 6:30 | 10:28 | 9.2 | 32:30 | 1:05:00 | 2:17:08 | 4:34:16 |
| 7:00 | 11:16 | 8.6 | 35:00 | 1:10:00 | 2:27:41 | 4:55:22 |
| 7:30 | 12:04 | 8.0 | 37:30 | 1:15:00 | 2:38:14 | 5:16:28 |
| 8:00 | 12:52 | 7.5 | 40:00 | 1:20:00 | 2:48:47 | 5:37:34 |
| 9:00 | 14:29 | 6.7 | 45:00 | 1:30:00 | 3:09:53 | 6:19:45 |
| 10:00 | 16:06 | 6.0 | 50:00 | 1:40:00 | 3:30:59 | 7:01:57 |
Standard race distances used throughout this page are 5 km, 10 km, the half marathon at 21.0975 km and the marathon at 42.195 km. The marathon is exactly twice the half marathon distance, so a marathon at the same pace takes exactly twice as long as the half.
Marathon pacing: even, negative and positive splits
Many runners find the second half of a marathon much harder than the first, so pacing choices matter more here than at shorter distances. Three patterns are discussed most often.
- Even pace: the same pace throughout. It is the easiest plan to execute and check against a watch at every 5 km mark.
- Negative split: the second half is run faster than the first. A modest version is to start about 1 percent slower than the average and finish about 1 percent faster, as in the right-hand column below.
- Positive split: the first half is faster than the second. This is rarely a plan; it is usually what happens after starting too fast, and a second half that is several minutes slower is often read as a sign of that.
| Goal time | Average pace /km | 10 km | Half | 30 km | 40 km | Negative split: first / second half pace |
|---|---|---|---|---|---|---|
| 3:00:00 | 4:16 | 42:40 | 1:30:00 | 2:07:59 | 2:50:38 | 4:19 / 4:13 |
| 3:30:00 | 4:59 | 49:46 | 1:45:00 | 2:29:18 | 3:19:05 | 5:02 / 4:56 |
| 4:00:00 | 5:41 | 56:53 | 2:00:00 | 2:50:38 | 3:47:31 | 5:45 / 5:38 |
| 4:30:00 | 6:24 | 1:03:59 | 2:15:00 | 3:11:58 | 4:15:57 | 6:28 / 6:20 |
| 5:00:00 | 7:07 | 1:11:06 | 2:30:00 | 3:33:18 | 4:44:24 | 7:11 / 7:02 |
| 5:30:00 | 7:49 | 1:18:12 | 2:45:00 | 3:54:37 | 5:12:50 | 7:54 / 7:45 |
The last column runs the first half at 101 percent and the second half at 99 percent of the average pace. Because both halves are the same length, the finish time equals the even-pace time exactly. For a 4-hour goal (average 5:41/km) that means about 5:45 for the first half and 5:38 for the second. A difference that small is hard to feel by effort alone, so a practical interpretation is simply to hold back by 5 to 10 seconds per km over the first 5 km. On hilly courses, a steady effort usually matters more than a steady pace, and your split times will follow the terrain. For effort ranges based on heart rate, see the Heart Rate Zone Calculator.
Predicting other distances: Riegel and VDOT
Several formulas estimate a time at one distance from a recent result at another. This page shows two of them.
- Riegel formula: T₂ = T₁ × (D₂ ÷ D₁)1.06. It is an empirical rule saying that doubling the distance more than doubles the time, by a factor of 21.06 ≈ 2.085, about 4 percent more than simple proportion.
- Daniels-style VDOT: based on the oxygen-cost and endurance-drop-off formulas published by Jack Daniels and Jimmy Gilbert. For speed v in metres per minute and time t in minutes, oxygen cost = −4.60 + 0.182258v + 0.000104v², sustainable fraction = 0.8 + 0.1894393e−0.012778t + 0.2989558e−0.1932605t, and VDOT = oxygen cost ÷ sustainable fraction. The VDOT shown here is a performance index derived from your result, not a laboratory measurement of VO₂max.
Worked check. A 10 km result of 50:00 means 200 m per minute for 50 minutes, giving a VDOT of about 40.0, and the Riegel formula predicts the following.
| Distance | Predicted time | Average pace /km |
|---|---|---|
| 5K | 23:59 | 4:48 |
| 10K (the reference result) | 50:00 | 5:00 |
| Half marathon (21.0975 km) | 1:50:19 | 5:14 |
| Marathon (42.195 km) | 3:50:01 | 5:27 |
As a second example, a 5K in 25:00 gives 10K in 52:07, half marathon in 1:55:00 and marathon in 3:59:47 by the same formula (VDOT about 38.3). Such predictions assume you have trained for the longer distance as thoroughly as you did for the one you ran.
Limits of race predictions
- Accuracy falls as the distance gap grows. Predicting a marathon from a 5K result is far less reliable than predicting a half marathon from a 10K, because the marathon depends heavily on weekly mileage, fueling and muscular endurance, not only on speed.
- Conditions matter. A result from a hot day or a hilly course does not transfer to a flat, cool race. Heat in particular tends to slow people noticeably.
- Use all-out race results. A training run done easy, or done while tired, does not represent what you can race.
- VDOT here is only a number. It is calculated from the formula above and does not replace the training pace tables in the original book. Consult that source for pace zones.
Common mistakes
- Trusting GPS distance blindly. A watch can read 10.2 km for a certified 10 km course, which makes your pace look faster than your official result. Enter the official distance for races.
- Mixing up input formats. "50:00" is fifty minutes, "1:30:00" is one hour thirty. A value such as "5000" without colons is rejected with an error message.
- Including stops. Counting traffic-light waiting time in a casual run makes pace look slower than your moving pace.
- Applying running pace to other sports. Swimming is normally quoted per 100 m, and cycling in speed. Use the right unit for the sport.
Using the numbers sensibly
Pace is a way to describe a run, not a prescription. Some people use race pace as an anchor and run most of their sessions noticeably slower than it, keeping a small number of harder efforts, but how much easy running and hard running suits you depends on your history, health and goals. Nothing on this page is medical advice or a coaching plan; a qualified coach or a doctor can tailor targets to you. For related energy estimates, try theExercise Calorie Calculator, the Steps to Calories Calculator or theBMR and TDEE Calculator.
When not to rely on this tool
An average pace says little about interval sessions where speed changes sharply between repetitions; enter each repetition separately instead. Do not push toward a target pace if you are injured or feeling chest pain or dizziness. All predictions are for reference only. Your calculations run entirely in your browser and nothing is sent to a server.
Frequently Asked Questions
What format should I use for the time?
Use "mm:ss" (for example 50:00) or "h:mm:ss" (for example 1:30:00). Seconds must be below 60, and so must minutes in the three-part form. Decimal seconds such as 24:59.5 are accepted.
What happens if I fill in all three boxes?
The values might contradict each other, so the tool asks you to leave one box empty. Leave blank the value you want to calculate.
What pace should a beginner aim for?
There is no single right answer. A pace where you can still talk in short sentences is a common starting point, and many new runners begin somewhere in the 6 to 8 minutes per km range. Mixing walking with running is fine; breathing and duration are more useful guides than the number.
Why does my real race differ from the Riegel prediction?
The formula assumes you are equally prepared for the new distance. Low weekly mileage, heat or a hillier course usually make half marathon and marathon results slower than predicted.
Is treadmill speed the same as outdoor pace?
The arithmetic is identical, but a treadmill has no wind resistance, so the same speed often feels easier. Some runners set a small incline to compensate, though how much is needed varies by person and machine.
Why show pace per mile?
Many race organisers, apps and training plans in the United States and the United Kingdom work in miles. For reference, 5:00/km is about 8:03/mile and 6:00/km is about 9:39/mile.
Related tools
- Heart Rate Zone Calculator - heart rate ranges for easy and harder efforts
- Exercise Calorie Calculator - estimated energy use by activity
- Steps to Calories Calculator - walking energy from step counts
- Unit Converter - convert km, miles and other units