Convert between pace and speed with race time predictions
Race predictions use the Riegel formula and assume consistent training. Actual race times depend on terrain, weather, nutrition, and fitness. Consult a running coach for personalised training plans.
Whether you are training for your first parkrun, preparing for a half marathon, or simply trying to understand your running performance, knowing your pace is essential. Pace -- the time it takes to cover a unit of distance -- is the most common way runners measure and communicate their speed. In the UK and most of Europe, pace is typically expressed in minutes per kilometre, while in the United States it is more common to use minutes per mile. Understanding your pace helps you plan training sessions, set realistic race goals, and track your fitness improvements over time. Running pace and speed are inversely related but each serves a different purpose. Pace (minutes per kilometre or mile) is more intuitive for runners because it directly relates to the experience of running: you can feel whether you are running at a 5:00/km pace versus a 6:00/km pace. Speed (kilometres or miles per hour) is more useful for comparison with other activities, such as cycling or driving, and is the standard measure in sports science and treadmill settings. This pace calculator converts between pace and speed in both metric and imperial units, and goes further by predicting your race times for standard distances using the well-established Riegel formula. By entering your time for any known distance -- whether it is a 5K parkrun time, a 10K race, or even a training run -- the calculator estimates how long it would take you to complete a 5K, 10K, half marathon (21.1 km), and full marathon (42.2 km). These predictions assume consistent training and are widely used by running coaches and race planners across the UK. The calculator is particularly useful for parkrun regulars looking to gauge their potential over longer distances, or marathon runners wanting to set appropriate pacing strategies for race day.
To calculate your running pace and race predictions: 1. Enter the distance you ran or plan to run. The default is 5 km (a standard parkrun distance). You can enter any distance -- a training run, race distance, or interval session. 2. Select the distance unit. Choose kilometres (default for UK runners) or miles. 3. Enter your time. Input the hours, minutes, and seconds it took (or you expect it to take) to cover the distance. For a 5K, you might enter 0 hours, 25 minutes, 0 seconds. 4. Review your results. The calculator shows your pace per kilometre and per mile, your speed in km/h and mph, and predicted race times for 5K, 10K, half marathon, and marathon distances. The bar chart visualises the predicted times for easy comparison. 5. Use the predictions wisely. Race predictions are estimates based on the Riegel formula. They assume equivalent training and fitness across distances. If you are stepping up to a new distance, consider adding 5-10% to the predicted time for a more conservative goal.
The pace calculator uses straightforward arithmetic for pace and speed conversion, and the Riegel formula for race predictions. Pace calculation: Total seconds = hours x 3600 + minutes x 60 + seconds Pace (seconds per km) = total seconds / distance in km Speed (km/h) = distance in km / (total seconds / 3600) For example, running 5 km in 25:00 (1,500 seconds): Pace = 1,500 / 5 = 300 seconds per km = 5:00/km Speed = 5 / (1,500 / 3,600) = 5 / 0.4167 = 12.0 km/h Pace per mile = 300 x 1.60934 = 484 seconds = 8:03/mile Race time predictions use the Riegel formula: T2 = T1 x (D2 / D1) ^ 1.06 Where T1 is your known time, D1 is the known distance, D2 is the target distance, and the exponent 1.06 accounts for the natural slowdown over longer distances due to accumulated fatigue. For example, from a 25:00 5K, the predicted 10K time would be: 25:00 x (10 / 5) ^ 1.06 = 25:00 x 2.0849 = 52:07. The Riegel formula was published by Pete Riegel in 1977 and remains one of the most widely used prediction models in distance running. It is reasonably accurate for distances between 1,500 metres and the marathon for trained runners.
Parkrun, the free weekly 5K timed run held every Saturday morning across the UK, is an excellent way to establish your baseline pace and track improvements. With over 700 events in the UK alone, there is likely one near you. Remember that race-day performance depends on many factors beyond fitness, including course profile (hills versus flat), weather conditions, nutrition and hydration strategy, and race-day nerves. Treadmill paces may also differ from outdoor paces due to the lack of wind resistance and the assistance of the moving belt.