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Enter a recent race result to predict your time at another distance: T2 = T1 × (D2/D1)1.06
Predictions are estimates. The Riegel formula assumes similar fitness and conditions across races.
Ask any experienced runner their secret and you will hear the same answer: pacing. Run the first kilometer too fast and you will crawl across the finish line; run it too slow and you leave minutes on the table. Our free Running Pace Calculator takes the guesswork out of pacing with instant conversions between pace, speed, distance and time — plus science-based race time predictions.
Whether you are training for your first 5K, chasing a marathon personal best, or just curious how fast that "easy 30-minute jog" really was, this tool gives you answers in seconds. Switch between kilometers and miles, pick from preset race distances or enter a custom one, and convert in both directions: time + distance → pace, or pace + distance → predicted finish time.
Everything runs instantly in your browser — no sign-up, no app, no subscription. Just numbers that make you a smarter runner.
Runners talk about pace (time per unit of distance, e.g. 5:30 min/km), while most of the world thinks in speed (distance per unit of time, e.g. 10.9 km/h). They are two sides of the same coin:
The calculator converts between all of these instantly, and formats pace the way runners read it — minutes:seconds per kilometer or per mile. No more mental arithmetic at the track.
Running is one of the few sports split between two measurement systems: most of the world races in kilometers, while the US (and UK road signs) think in miles. The calculator has a one-tap unit toggle, converting with the exact factor 1 mile = 1.60934 km.
A 8:00 min/mile pace, for example, equals 4:58 min/km — noticeably quicker than it sounds in miles. If you follow an American training plan but race locally in kilometers (or vice versa), the toggle keeps every workout and race plan consistent. Preset distances include 5K, 10K, half marathon (21.0975 km) and marathon (42.195 km), plus a custom distance field for anything from a 1-mile time trial to an ultramarathon.
Both modes show full breakdowns, including per-kilometer (or per-mile) splits, so you know exactly what each section of the race should feel like. Fueling those training kilometers properly matters too — dial in your nutrition with our macro calculator.
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Here is where it gets exciting. Sports scientist Peter Riegel discovered that race performances follow a predictable curve: T2 = T1 × (D2/D1)^1.06, where T1 is your known time over distance D1, and T2 is your predicted time over distance D2.
Worked example: you run 5K in 25:00 (1,500 seconds) and want to predict your 10K. T2 = 1500 × (10/5)^1.06 = 1500 × 2^1.06 ≈ 1500 × 2.085 ≈ 3,128 seconds ≈ 52:08. Notice the prediction is a little slower than simply doubling — that 1.06 exponent captures the reality that pace fades slightly as distance grows.
The calculator applies the Riegel formula automatically: enter one recent race result and get predicted times for every standard distance. It is remarkably accurate for trained runners — typically within a few percent — though it assumes equivalent training and conditions. Predictions get less reliable when jumping more than about double the distance (a 5K time will not perfectly predict a marathon without the long runs to back it up).
Staying hydrated is part of pacing too — long runs demand a fluid plan, so check our water intake calculator before your next big session.
Most beginners run 5K between 30 and 40 minutes (6:00–8:00 min/km). There is no "should" — a good pace is one you can hold while still being able to speak in short sentences. Consistency beats speed in your first months.
Very good for distances within about double your reference race, assuming similar fitness and conditions — usually within 2–5%. It is less reliable for huge jumps (5K → marathon) or hilly/trail courses, where terrain matters more than the math.
Use pace (min/km) for running — it maps directly to race timing and splits. Speed (km/h) is more useful on treadmills and for cycling. This calculator speaks both fluently.
Treadmills lack wind resistance and assist leg turnover with the moving belt, so the same effort often reads 10–20 seconds/km faster indoors. Set treadmill incline to 1% to better simulate outdoor running.
Use the Riegel prediction mode: enter your marathon time and it estimates your 5K potential (and vice versa). Just remember the formula assumes you have trained appropriately for the target distance.
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