A pace per mile calculator is the most direct tool a runner using US or UK distances needs. Whether you are training for a 5K, a half marathon, or your first marathon, every race plan eventually comes back to one number: your minutes and seconds per mile. This calculator solves that number from any pair of inputs — distance plus time, distance plus pace, or time plus pace — and immediately extends the result into a full set of training data: equivalent pace per kilometre, miles per hour, kilometres per hour, a complete per-mile split table, and race-time predictions for eight standard distances.
Everything runs entirely in your browser. No data is uploaded, no account is needed, and the answer updates as you type.
How it works
The core formula
Pace per mile is a simple ratio expressed in time notation:
Pace (min/mi) = Total time (seconds) ÷ Distance (miles)
The result in seconds is then split into minutes and leftover seconds and displayed as m:ss. For example, a half marathon (13.1 miles) run in 1 hour 45 minutes (6,300 seconds) gives:
6,300 ÷ 13.1 = 481.3 sec/mi = 8:01 /mi
The same division is inverted to solve for time or distance when those are the unknowns:
- Finish time = Pace (sec/mi) × Distance (miles)
- Distance = Total time (seconds) ÷ Pace (sec/mi)
Speed conversions
Pace and speed are reciprocals measured per hour versus per mile:
mph = 3600 ÷ pace (seconds per mile)
A 9:00 /mi pace converts to 3600 ÷ 540 = 6.67 mph. Multiply by 1.609344 to get km/h.
Pace per kilometre is derived by dividing seconds per mile by 1.609344 (the number of kilometres in a mile):
Pace /km = Pace /mi ÷ 1.609344
An 8:00 /mi pace becomes 480 ÷ 1.609344 = 298 sec/km = 4:58 /km.
Per-mile splits
The split table assumes perfectly even effort: every mile is run at exactly the calculated pace. This is the ideal training target. In practice your actual splits will vary slightly, but the even-split table is the standard pacing plan used on most race-day wristbands and GPS watches.
Race predictions (Riegel model)
The race predictions use Riegel’s 1977 endurance formula:
T&sub2; = T&sub1; × (D&sub2; / D&sub1;)^1.06
where T&sub1; is your known finish time at distance D&sub1; and T&sub2; is the predicted time at a new distance D&sub2;. The exponent 1.06 is empirically derived and reflects the fact that longer races are physiologically harder than a simple linear extrapolation would suggest — your pace per mile must slow as distance increases.
The model is well-calibrated for distances within roughly a factor of two of your reference run. Predicting a marathon from a 1-mile time trial, for instance, will overestimate your marathon fitness.
Worked example
A runner completes a 10K (6.2138 miles) in 52 minutes (3,120 seconds).
- Pace per mile = 3,120 ÷ 6.2138 = 502 sec = 8:22 /mi
- Pace per km = 502 ÷ 1.609344 = 312 sec = 5:12 /km
- Speed = 3600 ÷ 502 = 7.17 mph = 11.53 kph
- Predicted half marathon = 3120 × (13.1 / 6.2138)^1.06 = ~6,879 sec = 1:54:39
| Race | Predicted time | Pace /mi |
|---|---|---|
| 5K | 24:56 | 8:02 /mi |
| 10K | 52:00 | 8:22 /mi |
| Half marathon | 1:54:39 | 8:45 /mi |
| Marathon | 3:59:13 | 9:07 /mi |
Notice how the predicted marathon pace is 45 seconds per mile slower than the 10K pace — exactly the kind of realistic expectation Riegel’s model builds in. Runners frequently overpace marathons by ignoring this drift.
Formula reference
| Goal | Formula |
|---|---|
| Pace per mile | T (sec) ÷ D (miles) |
| Finish time | Pace (sec/mi) × D (miles) |
| Distance | T (sec) ÷ Pace (sec/mi) |
| mph | 3600 ÷ Pace (sec/mi) |
| Pace /km | Pace (sec/mi) ÷ 1.609344 |
| Race prediction | T&sub1; × (D&sub2; / D&sub1;)^1.06 |