Running Pace Calculator

Runners ask the same three questions over and over: how fast do I need to go, how long will it take, and how far did I actually run? This calculator answers whichever one you pick. Give it any two of distance, time and pace and it fills in the third, then shows your pace per kilometre and per mile, your speed in km/h and mph, and the speed to set on a treadmill.

It goes further than a one-line answer. A split table lists the time for every kilometre or mile, with an option for a negative split, where the second half is run a little faster than the first, which is how most good races are paced. A race predictor takes your result and estimates your 5K, 10K, half marathon and marathon times with Riegel’s formula, the method most running coaches and apps start from. There is also a small converter that turns a treadmill speed into a pace you can carry outside.

Times can be typed the way you would say them: 25:00, 1:45:30, 50m or 1h 45m. Everything is worked out by your browser, so nothing you enter is sent anywhere or saved.

1. Choose what to work out at the top: “Find pace”, “Find time” or “Find distance”. The box with the “Answer” tag fills itself in.
2. Pick km or miles. Choose a race from the list (5K, parkrun, 10K, half marathon, marathon, 1 mile) or type your own distance.
3. Type the other value: a finish time like 25:00 or 1:45:30, or a pace like 5:00 per km.
4. Read your pace, speed and treadmill setting, then check the race predictor and the split table. Switch to “Every mile” or “Negative split” if you want.
5. Tap “Copy result” or “Copy splits” to paste them into a note, a training plan or a pace band.

• Solves for pace, finish time or distance from the other two, live as you type.
• Kilometres or miles, with pace per km and per mile and speed in km/h and mph always shown together.
• Race presets: 5K, parkrun, 10K, half marathon (21.0975 km), marathon (42.195 km) and 1 mile, or any custom distance.
• Flexible time entry: 25:00, 1:45:30, plain minutes such as 50, or 1h 45m 30s.
• Split table for every km or mile, with a shorter final split shown properly and the running total beside each one.
• Negative split plans: choose how much faster the second half should be (up to 20%) and see both halves.
• Race predictor for 5K, 10K, half marathon and marathon using Riegel’s formula.
• Treadmill speed to pace converter, with a one-tap “Use this pace above”, and copy buttons for results and splits.

• For a race, a negative split of 1–3% is a sensible plan. Going out too fast in the first kilometres costs far more time later than it saves.
• Use a recent, all-out race for the predictor, not a training run. A parkrun or 10K from the last six weeks works well.
• Predictions for the marathon assume you have done the long runs. If your longest run is under about 30 km, add 5–10% to the predicted time.
• Hills, heat and wind all slow you down. On a hot day or a hilly course, plan to run 10–20 seconds per km slower than your flat-course pace.
• Paste the split table into a note on your phone, or write the halfway time on your hand. It is the most useful single check during a race.