What the pace calculator does
The pace calculator handles the three questions every runner asks, in one tool. Give it any two of distance, time and pace, and it solves for the third. It then shows your pace in both minutes per mile and minutes per kilometre, your speed in mph and km/h, and predicted finish times for the four standard race distances — 5K, 10K, half marathon and marathon — all updating live as you type.
The three modes
- Find pace: enter distance and time (you ran 5 miles in 40 minutes) to get your pace (8:00 per mile).
- Find time: enter distance and a target pace to get the finish time (a marathon at 9:00/mile takes about 3:55:58).
- Find distance: enter time and pace to get how far you went (45 minutes at 9:00/mile is 5 miles).
Pace vs. speed
Runners think in pace — minutes per mile or kilometre — because it maps directly to how a run feels and to race goals. Treadmills, cyclists and cars use speed — distance per hour. They are reciprocals: pace (in hours per mile) = 1 ÷ speed (in miles per hour). An 8:00 min/mile is 7.5 mph; a 5:00 min/km is 12 km/h. The calculator shows both so you can set a treadmill from a pace goal or read your watch either way.
Converting between miles and kilometres
One mile is 1.609 kilometres. To convert a per-mile pace to per-km, divide by 1.609; to go the other way, multiply by 1.609. So 8:00/mile ÷ 1.609 ≈ 4:58/km. This matters for runners who train with a metric watch but race in miles, or vice versa, and for comparing times across countries.
How to read the race predictions
The finish-time table assumes you hold the entered pace for the entire distance — an "even split". That is realistic for a 5K or 10K if the pace is appropriate, but most runners fade over a half or full marathon, so the longer predictions are best-case even-split targets rather than guarantees. They are most useful as a sanity check: if your goal-marathon pace would require holding your current 5K pace for 26.2 miles, the table makes that ambition obvious.
Training smart with pace
A classic mistake is running every session at race pace. Endurance research strongly favours mostly easy running — a conversational pace where you could speak in full sentences — with a smaller dose of faster tempo and interval work. This "80/20" distribution builds aerobic fitness while limiting injury and burnout. Use the calculator to set easy, tempo and interval paces from a recent race result.
Use with the other tools
Pair pace work with the calories burned calculator to estimate energy used on a run, and the calorie calculator to fuel training. For hydration around long runs, see the water intake calculator.