Whether you’re training for a 5K or chasing a marathon PR, this calculator solves for whatever you’re missing — pace, time, or distance. Pick a preset race or enter a custom distance, and see split times for every mile or kilometer.
Pro tip: Most runners finish faster with a negative split strategy — starting slightly slower than goal pace and picking up speed in the second half. Use the premium negative split planner to see target splits for each mile.
Based on your current distance and time, predict finish times for other races using Riegel’s formula.
Start 5% slower than goal pace, finish 5% faster. See your ideal split for every mile or km.
| Split | Target Pace | Split Time | Cumulative |
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How to Use the Pace Calculator
Choose what you want to solve for: Find Pace if you know your distance and time, Find Time if you know your pace and distance, or Find Distance if you know your pace and time. Enter the two known values, and the third is calculated instantly. Toggle between miles and kilometers, or tap a race preset to auto-fill a standard distance.
Understanding Running Pace
Pace is the inverse of speed — instead of “miles per hour,” runners think in “minutes per mile.” An 8:00/mi pace means you cover one mile every eight minutes. This framing is more intuitive for training because it directly maps to effort: you can feel the difference between 7:30 and 8:00 in your legs. Converting between min/mi and min/km is straightforward — multiply by 0.6214 to go from per-km to per-mi, or by 1.6093 for the reverse.
Common Race Distances
The standard road race distances are 5K (3.107 miles), 10K (6.214 miles), Half Marathon (13.109 miles / 21.0975 km), and Marathon (26.219 miles / 42.195 km). Each roughly doubles the previous one, but the effort increase is exponential. A runner who can do a 5K in 25 minutes typically can’t simply double it for a 50-minute 10K — fatigue adds roughly 5–8% per doubling of distance.
How Split Times Work
Splits break your total distance into individual mile or kilometer segments, showing the time for each segment and a running cumulative total. Even-paced running means every split is identical. In practice, most recreational runners start too fast and slow down (positive splits), which leads to an unpleasant final few miles. Tracking splits helps you learn to pace evenly and identify where your form breaks down.
Race Prediction with Riegel’s Formula
Riegel’s formula predicts race times based on a known performance at a different distance. The equation is T2 = T1 × (D2 / D1)^1.06, where the 1.06 exponent accounts for fatigue at longer distances. It’s remarkably accurate for distances between 5K and marathon for trained runners. If you ran a 25-minute 5K, the formula predicts roughly a 52-minute 10K, a 1:55 half marathon, and a 4:02 marathon. Subscribers see predictions for all four major race distances based on whatever distance and time they enter.
The Negative Split Strategy
A negative split means running the second half of a race faster than the first. Nearly every marathon world record has been run with negative splits. The strategy works because starting conservatively preserves glycogen stores and prevents the lactate buildup that causes “hitting the wall.” Our negative split planner starts you at 5% slower than goal pace and gradually accelerates to 5% faster, distributing the effort change evenly across all splits. Subscribers can see exact target times for each mile or kilometer.
Looking for related tools? Try our TDEE Calculator to match your calorie intake to your running mileage, or explore all Health & Fitness tools.