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Running Pace Calculator

Computes running pace in min/km and min/mile and speed in km/h and mph from a distance and elapsed time, and projects the finish time for 5 km, 10 km, half marathon and marathon at that constant pace.

When to use

You know a distance and the time it took (or a target time) and need the pace, the equivalent speed, or the time that pace gives over standard race distances.

Do not use when: You want a realistic prediction of a longer race from a shorter one (pace slows with distance; use race-time-predictor), or you only need to convert between pace and speed units (use pace-converter).

Formula

pace_s_per_km = time_seconds / distance_km; pace_s_per_mile = pace_s_per_km × 1.609344; speed_kmh = 3600 / pace_s_per_km; speed_mph = speed_kmh / 1.609344; time(D) = pace_s_per_km × D for D = 5, 10, 21.0975, 42.195 km

Splits assume a perfectly even pace; they are not race predictions. Distances follow World Athletics definitions (half marathon 21.0975 km, marathon 42.195 km).

Inputs

Parameter	Type	Required	Description
`distance`	number	yes	Distance covered, in the unit given by distance_unit. Range: > 0, ≤ 5000
`distance_unit`	enum: km \| mi	default km	Unit of the distance input.
`time`	string	yes	Elapsed time as h:mm:ss (1:45:00), mm:ss (50:00) or plain minutes (50).

Outputs

Output	Type	Unit	Description
`pace_min_per_km`	string	min:sec/km	Minutes and seconds per kilometre.
`pace_min_per_mile`	string	min:sec/mi	Minutes and seconds per mile.
`pace_seconds_per_km`	number	s/km	Same pace as a plain number of seconds per kilometre.
`speed_kmh`	number	km/h	Average speed in kilometres per hour.
`speed_mph`	number	mph	Average speed in miles per hour.
`distance_km`	number	km	Input distance converted to kilometres.
`time_5k`	string	h:mm:ss	Time to run 5 km at exactly this pace.
`time_10k`	string	h:mm:ss	Time to run 10 km at exactly this pace.
`time_half_marathon`	string	h:mm:ss	Time for 21.0975 km at exactly this pace.
`time_marathon`	string	h:mm:ss	Time for 42.195 km at exactly this pace.

Example

10 km in 50:00: {"distance":10,"distance_unit":"km","time":"50:00"} → {"pace_min_per_km":"5:00","pace_min_per_mile":"8:03","pace_seconds_per_km":300,"speed_kmh":12,"speed_mph":7.46,"time_5k":"0:25:00","time_half_marathon":"1:45:29","time_marathon":"3:30:59"}

5 miles in 45:00: {"distance":5,"distance_unit":"mi","time":"45:00"} → {"pace_min_per_mile":"9:00","pace_min_per_km":"5:36","speed_mph":6.67,"speed_kmh":10.73,"time_10k":"0:55:55"}

GET https://tttkmbb.com/api/v1/calculate/running-pace?distance=10&distance_unit=km&time=50%3A00

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/running-pace (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/running-pace · Markdown: https://tttkmbb.com/fitness/running-pace.md · JSON definition: https://tttkmbb.com/fitness/running-pace.json
MCP: server https://tttkmbb.com/mcp, tool calculate_running_pace
OpenAPI operationId: calculate_running_pace
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

FAQ

How do I enter the time?

As h:mm:ss (1:45:00), mm:ss (50:00) or a plain number of minutes (50 or 50.5).

Why is my marathon split faster than what I could actually run?

The splits hold the pace constant. Real performance slows with distance; race-time-predictor applies Riegel's fatigue exponent to model that.

Related calculators

Race Time Predictor — Predict realistic finish times for other distances instead of constant-pace splits.
Pace Converter — Convert between min/km, min/mile, km/h and mph directly.
Heart Rate Zone Calculator — Pair pace targets with heart-rate training zones.