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Altitude Pace Adjustment Calculator

See what thin air will cost you on race day.

How it is calculated

The tool assumes no slowdown up to 300 m. Above that, pace slows by 2.5 % for every 1,000 m of extra height for a sea-level runner who is not acclimatised: slowdown % = (altitude − 300) / 1000 × 2.5 × factor. The factor is 1.0 for no acclimatisation, 0.7 for partial and 0.5 for full. Adjusted pace is sea-level pace × (1 + slowdown / 100); time lost is the pace difference times distance. Altitude is in metres (0 to 6,000), pace is decimal minutes per km at sea level (5.5 means 5:30) and distance is in km. The 'oxygen' line shows air pressure as a percent of sea level from the barometric formula; it is for information and does not change the slowdown.

Worked example

Race in a city at 2,240 m, sea-level pace 5.0 min/km (5:00), 10 km, not acclimatised. Height above 300 m: 2,240 − 300 = 1,940 m. Slowdown: 1.94 × 2.5 = 4.85 %. Adjusted pace: 5.0 × 1.0485 = 5.2425 min, shown as 5:15 /km. Adjusted time: 5.2425 × 10 = 52.4 minutes, or 52:26, so 2:26 is lost. Air pressure there is 76.1 % of sea level. With partial acclimatisation the slowdown falls to 3.40 %.

Try this example →

Common mistakes

  • Typing the pace as 5.30 for 5:30. The field is decimal minutes, so 5.30 is 5 minutes 18 seconds; use 5.5.
  • Entering altitude in feet. The field is metres, and 7,350 ft is 2,240 m.
  • Choosing full acclimatisation after a few days at altitude. The 'full' setting halves the slowdown, so it understates the cost for a recent arrival.
  • Treating the oxygen percentage as the pace penalty. It describes air pressure and is separate from the slowdown percentage.
  • Using a pace already measured at altitude. The input must be your sea-level pace; otherwise the penalty is applied twice.

About this calculator

Air at altitude has lower barometric pressure, which reduces the partial pressure of oxygen available to your lungs and blood, cutting into the oxygen delivery that fuels aerobic running — the higher you go, the smaller each breath's oxygen payload becomes. The effect is small below about 300 m; above that it grows in a straight line, at roughly 2.5% slower pace per 1,000 m of extra elevation before acclimatisation, while partial acclimatisation over days to weeks lets the body compensate somewhat through increased red blood cell production and breathing efficiency.

Runners racing or training at elevation — from mountain trail races to simply visiting a higher-altitude city — use altitude pace adjustment to avoid starting a race at sea-level effort and blowing up, translating a goal pace into a realistic altitude-adjusted pace and finish time instead. Coaches also use it to set fair expectations for athletes traveling from sea level to compete at venues like Mexico City or Colorado mountain races.

Starting from your sea-level pace and the race distance, it uses the altitude you will race at and how acclimatised you are to estimate how much thinner air will slow your pace and finish time.

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