Running Pace Calculator | Solve Distance, Time, or Pace from the Other Two

Enter any two of distance, time, and pace, and this calculator solves for the third. It includes 5K/10K/half/full presets, a per-mile/km split table, and a min/km ↔ min/mile toggle, so you can plan race-day pacing before you line up.

💡 About this tool

• Reverse-engineer the pace you need Got a goal time like "sub-2:00 half marathon"? Enter the time and distance, and the tool returns the pace per kilometer (or per mile) you have to hold. Flip it around and it predicts your finish time from a known pace.
• A split table you can actually race off Instead of one number, you get a row-by-row breakdown: lap time and cumulative elapsed time at every kilometer. Tape the 5K/10K/15K splits to your wrist and you can tell at a glance whether you went out too hot.
• From the 5K parkrun to the marathon The 5K/10K/half/full buttons set the distance in one tap, and Custom handles the oddballs — a 10-miler, a 30K long run, or a 400 m track rep.

🧐 Frequently Asked Questions

Q. What's the difference between pace and speed?

A. Pace is time-based — how many minutes and seconds to cover one kilometer or mile — and it's what most runners and watches report. Speed is distance-based (km/h or mph). They describe the same effort: 5:00/km is the same as 12 km/h. This tool works in pace because that's what shows up on race bibs and training plans.

Q. How does the min/km ↔ min/mile toggle work?

A. Tapping the pace-unit button swaps both the pace input fields and the displayed result between min/km and min/mile. Handy if you're targeting a US race that posts mile splits or your treadmill reads in miles. Distance always stays in km; the tool converts internally and only re-labels the pace.

Q. Why do I uncheck one field instead of typing all three?

A. Distance, time, and pace are tied by a single relationship — pace = time ÷ distance — so once two are fixed, the third is determined. Letting you type all three at once would create contradictions, so you uncheck the value you want the tool to compute and feed it the other two.

📚 Fun Facts

Even pacing beats heroics. Analyses of major-marathon finish data keep showing that runners who hold a steady or slightly faster second half ("negative split") tend to hit their goal times, while big early surges usually end in a painful fade. The famous sub-2-hour marathon attempt was paced to roughly 2:50/km the whole way — relentlessly even. Use the split table to sanity-check your plan: if your early kilometers are wildly faster than your target average, that's a red flag long before the wall.