How the conversion works
The calculator implements two published models. The default is Jack Daniels' rule of thumb for aerobic racing at altitude: roughly 4 to 5 seconds of slowdown per mile of race distance per 1,000 feet of elevation above 3,000 feet. This tool uses the midpoint, 4.5, and applies no adjustment at or below 3,000 feet. Because the rule is additive in pace, the penalty scales directly with race distance: double the distance, double the seconds lost.
The second option comes from Bassett et al. (1999), published in Medicine and Science in Sports and Exercise. Bassett and colleagues fitted polynomial curves to physiological data describing the percentage of sea-level aerobic power available at a given elevation, with separate curves for acclimatized athletes (several weeks at altitude) and non-acclimatized athletes (1 to 7 days). The calculator applies that percentage as a multiplicative factor on your time, on the assumption that speed in a predominantly aerobic race is proportional to available aerobic power.
Acclimatization matters more than most runners expect. A lowlander who flies in and races within 24 to 48 hours of arrival performs closer to the non-acclimatized curve, which predicts a substantially larger penalty. Living or training at altitude for several weeks moves you toward the acclimatized curve. Altitude's cost also grows with race duration: the longer the event, the larger the aerobic contribution, so a marathoner gives up far more total time than a miler at the same venue.
What this is not
These are not the official NCAA conversion tables. The NCAA published fixed per-event conversions for track races at altitude venues, and it voted in 2025 to drop altitude conversions from championship qualifying altogether. The NCAA figures subtract less than the physiological models here, partly because they also credit altitude-team adaptation and event-specific anaerobic contribution. More broadly, published models disagree with each other by several percent at 7,000 feet, so treat every conversion from this page, or any other, as an estimate with a real error bar, not a certified equivalent mark.
Worked example: a 20:00 5K at 7,000 feet
Say you run a 20:00 5K at 7,000 feet, roughly the elevation of Flagstaff, Arizona. Under the Daniels rule, the venue is 4,000 feet above the 3,000-foot threshold, so the adjustment is 3.107 miles times 4.5 seconds times 4, about 56 seconds, or 18 seconds per mile. Your sea-level equivalent is 19:04. Switch to Bassett acclimatized and the model estimates you had about 91 percent of your sea-level aerobic power available, so the same race converts to 18:10, a difference of 1:49. The spread between 19:04 and 18:10 for identical inputs is exactly why you should read any conversion as a range, not a single true number.
Who should not use this
Sprinters. Events of 400 meters and shorter actually get faster at altitude, because the thinner air reduces aerodynamic drag while the effort is overwhelmingly anaerobic and barely touched by the reduced oxygen. This calculator applies only to predominantly aerobic events, roughly 800 meters up to the marathon. Two other caveats: the Bassett model is distance independent and is best suited to races of 3,000 meters and longer, so it will overstate the penalty for an 800; and the Daniels rule is additive in pace, which means it penalizes faster runners slightly more in percentage terms, consistent with how Daniels framed the rule for trained runners.
Related tools and guides
Once you have a sea-level equivalent, feed it to the race time predictor to project that fitness across other distances, and use the pace calculator to turn the converted time into per-mile targets. Racing somewhere hot as well as high? The heat pace calculator estimates the additional slowdown from temperature and humidity.
Frequently asked questions
How much slower do you run at altitude?
Under the Daniels rule, figure 4 to 5 seconds per mile of race distance per 1,000 feet above 3,000 feet. At a 7,000-foot venue like Flagstaff, that is roughly 18 seconds per mile, or about 56 seconds over a 5K. The Bassett model, which works from the percentage of aerobic power you lose, predicts a larger penalty: nearly 1:50 on the same 5K for an acclimatized runner. Both are estimates, and individual responses vary widely.
Is this the official NCAA altitude conversion?
No. The NCAA published fixed per-event conversion tables for track races at venues of 3,000 feet and above, and those tables subtract less than the physiological models here because they also account for altitude-based teams and event-specific anaerobic contribution. The NCAA also voted in 2025 to drop altitude conversions from championship qualifying entirely. This calculator applies published physiological models, not the NCAA tables.
Do sprints slow down at altitude?
No, they speed up. Events of 400 meters and shorter are predominantly anaerobic, so the reduced oxygen barely matters, while the thinner air cuts aerodynamic drag. That is why sprint records set at altitude, most famously at the 1968 Mexico City Olympics, were faster than sea-level marks. This calculator is for aerobic events from roughly 800 meters to the marathon and should not be used for sprints.
How long does it take to acclimatize to altitude?
Meaningful acclimatization takes weeks. If you live at sea level and race at altitude within 24 to 48 hours of arriving, your performance sits closer to the non-acclimatized Bassett curve. After several weeks of living or training at altitude, blood and ventilatory adaptations move you toward the acclimatized curve, which predicts a smaller penalty at every elevation.
Which model should I choose?
Use the Daniels rule as a conservative default for trained runners; it is the simplest published guidance and this tool uses the midpoint coefficient of 4.5 seconds per mile per 1,000 feet. Choose Bassett acclimatized if you have lived at altitude for weeks, and Bassett not acclimatized if you flew in a day or two before the race. Comparing all three gives you an honest range rather than false precision.
Why does the effect grow with race distance?
Longer races are more aerobic, and altitude taxes exactly the aerobic system. A miler loses only a handful of seconds at 7,000 feet, a 5K runner loses closer to a minute, and a marathoner can lose several minutes. The Daniels rule builds this in directly, since its adjustment scales with the number of miles in the race.