Pace, time, distance, splits, and race-time predictions in one place.
Enter any two — the third will be calculated.
8:03
per mile
5:00 per km · 7.5 mph · 12.0 km/h
Enter a race time you've recently run. We'll predict your times at other distances using the Riegel formula.
Distance
Predicted Time
Pace/mi
Pace/km
Based on the Riegel formula: T₂ = T₁ × (D₂ / D₁)1.06. Most accurate within ±2× the input distance.
Enter your current 5K race pace. We'll calculate the training paces commonly used in Daniels/Pfitzinger-style plans.
Zone
Pace/mi
Pace/km
Use for
Enter your target finish time and we'll show what each mile or kilometer split should be.
Split
Cumulative Time
Pace
How pace, time, and distance relate
The three are bound together: pace = time ÷ distance. Know any two and you've got the third. Standard race distances:
Distance
Miles
Kilometers
Common target
5K
3.107
5.000
20:00 – 35:00
10K
6.214
10.000
40:00 – 1:10:00
Half Marathon
13.109
21.098
1:30 – 2:30
Marathon
26.219
42.195
3:00 – 5:30
About the Riegel race-time formula
Predicting a marathon time from a 10K isn't pure math — endurance, fueling, and pacing experience all matter. But Riegel's formula gives you a sane starting point:
T₂ = T₁ × (D₂ / D₁)1.06
The exponent 1.06 reflects that humans slow down slightly as distance grows. Use it to convert a recent honest race effort into a target for another distance, then adjust based on your training history. Predictions across very different distances (mile → marathon) are less reliable than similar ones (10K → half).
Training pace zones
Most structured training plans (Daniels, Pfitzinger, Hansons) prescribe different paces for different days. The four most common:
Easy — ~1:30–2:30/mi slower than 5K race pace. Conversational. Most of your weekly volume should be here.
Marathon — about 30–45 seconds/mi slower than half-marathon pace. "Comfortably hard" — used for long runs with quality.
Threshold — about 25–30 seconds/mi slower than 5K pace. "Comfortably uncomfortable" — pace you could hold for an hour all-out.
Interval — 5K pace or slightly faster. For 3–5 minute repeats with full recovery.
FAQ
How do you calculate running pace?
Divide total time by distance. For a 5K (3.1 miles) finished in 25 minutes: 25 ÷ 3.1 = ~8:04 per mile. Use the Pace Calculator tab above for any combination.
What is a good marathon pace?
Beginner: 11:00–13:00/mi (4:48–5:40 finish). Intermediate: 9:00–10:30/mi (3:55–4:35). Advanced: sub-8:00/mi (under 3:30). Elite: sub-5:00/mi. The honest answer is "whatever you can hold for 26.2 miles" — using the predictor with your recent 10K time gives you a realistic target.
How accurate is the Riegel race-time formula?
Within 2–4% for trained runners between similar distances. Less accurate going from a mile to a marathon, because at marathon distance, fueling and muscular endurance become limiting factors that the formula doesn't model.
What pace should I run my easy runs at?
1:30–2:30 per mile slower than your current 5K race pace. If your 5K pace is 8:00/mi, easy runs are 9:30–10:30/mi. The Training Paces tab calculates this automatically.
Should I train by pace or heart rate?
Both work. Pace is precise but ignores weather, sleep, and fatigue. Heart rate adjusts for those automatically but lags by 30–60 seconds and varies day-to-day. Many runners use pace targets but check heart rate to make sure they're not pushing too hard on easy days.
Why does my GPS watch show a different pace than I calculated?
GPS watches sample your position every second or two and estimate pace from the change. Sudden direction changes, tree cover, tall buildings, and tunnels all introduce error — usually 1–3% over a typical course. Track-based laps and certified race courses are the most accurate references.