Running Pace Calculator
Enter distance and time, or your target pace, to calculate pace, finish time, or distance — instantly and entirely in your browser.
Time
Please enter a time (0:00:00 is not valid)
Results are estimates only and do not constitute medical or sports science advice. Actual performance may vary significantly based on fitness level, course terrain, weather conditions, and individual factors. Always listen to your body.
How to Use
Choose one of three calculation modes using the tabs at the top. Pace Calculator computes your pace (min/km or min/mile) from distance and finish time. Finish Time predicts how long it will take to complete a given distance at your target pace. Distance tells you how far you can run in a given time at a given pace.
Use the preset buttons — 1 km, 5 km, 10 km, Half marathon, Full marathon — to fill in the distance field instantly. The unit toggle (km / mile) applies across all modes. When you switch units, preset values automatically reflect the selected unit, so Garmin or Apple Watch users in miles can work in their native unit.
Click 'Lap Split Table' to expand the lap table. It shows your cumulative time at every 1 km (or 1 mile) split, including a partial final lap (e.g., the last 0.195 km of a marathon). Use it to plan race-day pacing or to set pace alerts on your GPS watch.
How the Calculations Work
Pace calculation: Pace (sec/km) = Total time (sec) ÷ Distance (km), with the result truncated (floor) to whole seconds. Truncating rather than rounding means 'if you hold this pace, you are guaranteed to finish within your target time.' Finish time uses rounding: Finish time (sec) = Pace (sec/km) × Distance (km), rounded to the nearest second. Distance calculation: Distance (km) = Total time (sec) ÷ Pace (sec/km). The mile conversion constant is exactly 1.609344 km (International Yard and Pound Agreement, 1959; NIST SP 330).
Key insight A — converting between pace and speed: Many runners struggle to translate between the pace display on their GPS watch (min/km) and the speed display on a treadmill (km/h). There is a single formula: Speed (km/h) = 60 ÷ Pace (min/km decimal). For example, a 4:30/km pace equals 4.5 min/km, so speed = 60 ÷ 4.5 = 13.3 km/h. A 6:00/km pace is exactly 10.0 km/h. A sub-4 marathon (under 4 hours) requires a 5:41/km pace, which equals 10.6 km/h on a treadmill — a useful anchor number.
Key insight B — negative split strategy: Running the second half of a race slightly faster than the first is called a negative split, and research shows it correlates with better finish times. Most marathon world records have been set with a roughly 51:49 front-half to back-half ratio (source: NCBI — 'The physiology and psychology of negative splits'). Going out too fast drains glycogen and causes 'hitting the wall' around km 30–35. Use the Finish Time mode to find your goal pace, then plan front-half splits at goal pace +5–10 sec/km. The lap table lets you compare early vs. late splits visually.
FAQ
- What is the difference between pace and speed?
- Pace (min/km or min/mile) measures how long it takes to cover one unit of distance. Speed (km/h or mph) measures how far you travel in one hour. To convert: Speed (km/h) = 60 ÷ Pace (min/km). For example, a 5:00/km pace equals 12.0 km/h. GPS watches typically show pace; treadmills typically show speed.
- Should I run a half marathon at the same pace as a 10K?
- Generally no. A sustainable half marathon pace is around 10–20 sec/km slower than your 10K race pace for most runners. Individual fitness, training background, and race-day conditions all play a role. The calculator gives you a target to work from, but it is a simulation — not medical or coaching advice.
- What is a negative split and how do I use this tool for it?
- A negative split means running the second half faster than the first. It is associated with better race outcomes because it prevents burning through glycogen too early. Use the Finish Time mode to find your goal pace, then plan your front-half splits at goal pace plus 5–10 sec/km. The lap table shows cumulative times at each split so you can compare front vs. back halves side by side.
- How many km is a mile? What conversion factor does this tool use?
- Exactly 1.609344 km (International Yard and Pound Agreement, 1959; NIST Special Publication 330). A full marathon is 42.195 km = 26.219 miles (3 decimal places). The tool uses this exact constant for all unit conversions.
- What pace do I need for a sub-4 marathon?
- Here are the target paces for common marathon goals (calculated as floor(target seconds ÷ 42.195 km)): Sub-3 (under 3:00:00): 4:15 /km — Sub-3:30: 4:58 /km — Sub-4: 5:41 /km — Sub-5: 7:06 /km. Enter your target time in Pace Calculator mode with Full Marathon selected to verify these values.
- What is the partial lap at the bottom of the split table?
- A marathon is 42.195 km, which is not evenly divisible by 1 km. After 42 full kilometer splits, there is a remaining 0.195 km. This partial (fractional) lap is shown as the last row, highlighted in a different background color, with its actual distance shown in the Distance column.