Running Pace Calculator

Work out running pace, finish time, distance and split times, predict race results at any distance from one performance, and get VDOT training paces. Everything is computed offline from your input. No API key, no login, no scraping, nothing to break.

Give it a distance and a time and it returns pace per kilometre, pace per mile, pace per 400 m, speed in km/h and mph, an estimated VDOT, and a split table. Give it a race result and it returns predicted times at 17 standard distances plus the five Daniels training zones.

What it does

Seven calculation types, mixed freely in one run:

• pace gives pace and speed from a distance and a time.
• time gives finish time from a distance and a pace or speed.
• distance gives how far you go from a time and a pace or speed.
• splits builds a split table with even, negative or positive pacing.
• predict estimates race times at 800 m through 50 km from one result.
• training returns easy, marathon, threshold, interval and repetition paces.
• convert turns any pace or speed into every other representation.

Input

One object per calculation in the calculations array.

{
  "calculations": [
    { "type": "pace", "distance": "marathon", "time": "3:45:00", "splitEvery": 5, "unit": "km" },
    { "type": "time", "distance": 10, "unit": "km", "pace": "4:30", "paceUnit": "min/km" },
    { "type": "splits", "distance": "half marathon", "time": "1:45:00", "splitEvery": 5, "strategy": "negative", "strategyPercent": 2 },
    { "type": "predict", "distance": "5k", "time": "22:30" },
    { "type": "training", "distance": "5k", "time": "22:30" },
    { "type": "convert", "pace": "8:00", "paceUnit": "min/mi" }
  ]
}

Field notes:

• distance takes a number with unit (km, mi, m, yd, ft) or a name: marathon, half marathon, 10k, 5k, mile, 1500m, 10 mile, 50k and more.
• time takes 3:45:00, 22:30, 1h30m15s, 90m or a plain number of seconds.
• pace takes 4:30 with paceUnit set to min/km or min/mi. A plain number is read as minutes.
• speed takes a number with speedUnit of kph, mph or m/s.
• splitEvery sets the split interval in the calculation's unit, so 5 with unit km means 5 km splits.
• strategy is even, negative or positive, and strategyPercent sets how far the first and last splits sit from the average.
• weightKg adds an estimated calorie burn to every row.

Run-level settings cover all calculations: includeSplits, maxSplits, predictionMethod, riegelExponent and weightKg.

Output

One row per result. Summary rows carry the headline numbers, split rows carry one split each, prediction rows carry one target distance each, and training rows carry one zone each.

Field	Meaning
type, rowType, label	Which calculation and which kind of row
distance, unit, distanceKm, distanceMiles, distanceMeters	Distance in the requested unit and in every common unit
time, timeSeconds	Elapsed time
pacePerKm, pacePerMile, pacePer400m	Pace in mm:ss
speedKph, speedMph, speedMps	Speed
splitNumber, splitTime, cumulativeTime	Split table columns
vdot, vo2max	Estimated VDOT and oxygen cost
intensityPercent, paceRange	Training zone intensity and its pace band
predictionMethod, timeRiegel, timeCameron, timeVdot	All three prediction models side by side
caloriesBurned	Estimate, only when weightKg is set
error	Filled when one calculation fails, the rest still run

How the numbers are worked out

Pace, speed and split arithmetic are exact. Predictions use three published models so you can compare them:

• Riegel: T2 = T1 * (D2 / D1) ^ 1.06. The exponent is adjustable.
• Cameron: an empirical fit that holds from roughly 400 m to 50 km.
• VDOT: the Daniels and Gilbert oxygen-cost model, solved for the time at the target distance that gives the same VDOT as your input performance.

Training paces come from inverting the same oxygen-cost curve at each zone's share of VDOT. Against the published VDOT tables the model lands within a few seconds: VDOT 60 predicts a 35:22 10K, VDOT 50 predicts a 3:10:40 marathon.

These are estimates from one performance. Weather, hills, fitness on the day and how well you paced the effort all move the real result.

Use cases

• Build a pace band or wrist chart for a goal race.
• Check what a recent parkrun or time trial implies for a half marathon or marathon.
• Set training paces for a block without hunting through a printed table.
• Convert treadmill speed into outdoor pace.
• Generate split tables in bulk for a running club, a coaching sheet or a pace group.

Pricing

Pay per result. You are charged for the rows the run produces and nothing else.