Can this predict my marathon time from a 5K result?

It can project a flat pace × distance estimate, but real race performance slows over longer distances due to fatigue — a genuine prediction needs a dedicated model like Riegel's formula.

Why does pace per km differ from pace per mile?

A kilometer is shorter than a mile, so at the same running speed, you cover a kilometer in less wall-clock time than a mile.

What's the difference between pace and speed?

Pace is time per unit distance; speed is distance per unit time — mathematically reciprocal, just expressed differently.

Does this tool account for elevation or terrain?

No — it's a pure time/distance/pace calculation.

Why do the race-distance projections have a disclaimer?

They're simple pace × distance math at your entered pace, not an accurate race-time prediction.

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Health & Fitness

Running Pace Calculator

Solve for pace, time, or distance, with certified race-distance quick-picks.

🔒 Runs entirely in your browser — nothing here is ever uploaded

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Last reviewed 2026-08-30

About the Running Pace Calculator

Solves for any one of pace, finish time, or distance when you know the other two — using certified race distances (5K, 10K, half marathon, marathon) as quick-pick shortcuts, and keeps both mile and kilometer figures live regardless of which unit you're working in.

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How to use it

Choose what to solve for: pace, time, or distance.
Enter the two known values — a distance (or pick a standard race distance), and either a finish time or a target pace.
Read the solved value plus pace/speed in both mile and km terms.

Formula

Pace (min per unit) = time (min) ÷ distance. Time (min) = pace × distance. Distance = time (min) ÷ pace. Distances convert via 1 mile = 1.609344 km.

Worked example

A 5K (3.10686 mi) run in 25:00: solving for pace gives 8:03/mi (25 ÷ 3.10686), or exactly 5:00/km (25 ÷ 5) since 5K is exactly 5 kilometers by definition.

Certified race distances

Certified race distances
Race	Miles	Kilometers
5K	3.1069	5
10K	6.2137	10
Half marathon	13.1094	21.0975
Marathon	26.2188	42.195

Interpreting your result

Race-equivalent times shown are plain pace × distance projections at your current, unchanged pace — not a race-time prediction. Real performance typically slows over longer distances as fatigue sets in. Certified race distances used (5K, 10K, half marathon, marathon) match official distances to 4 decimal places, not the commonly rounded '13.1/26.2 miles' shorthand.

Recommendations

• Use the quick-pick race buttons to instantly fill in a certified distance rather than typing 13.1 or 26.2, which are rounded shorthand.
• Pace per km is always a smaller number than pace per mile at the same running speed.
• The 'at this pace, standard distances take' projections assume your pace never changes — real race times for longer distances are usually a bit slower than a flat linear projection.

Frequently asked questions

13.1 miles is a commonly used rounded shorthand — the certified distance is 13.1094 miles (21.0975 km).