What's a normal oxygen level in Denver?
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On a watch, a typical day in Denver runs about 93 to 98 and a typical night about 92 to 96 for a 40-year-old, 1 to 2 points under sea level. At 5,280 feet, each breath carries about 82% of the oxygen it would at the coast.
What we’d do
If you live in Denver, judge your nights against Denver’s range and your own usual nights. Awake and resting, 92 or lower is still a call to your doctor, wherever you live. If you’re visiting, Denver itself is below the CDC’s altitude risk line, and it makes a good first night before the mountains.
Why is it lower in Denver?
Denver is the Mile High City, and the mile has a spot. In 1909 surveyors put it on the 15th step of the State Capitol’s west steps, and “One Mile Above Sea Level” was carved there in 1947 after earlier plates were stolen. A 1969 survey moved it to the 18th step, and a 2003 survey to the 13th. In 2026 the National Geodetic Survey found it on the 17th step, using a new national elevation reference due to become official in 2027.
At that height the air is still about 21% oxygen, but there’s less air in each breath, about 82% of the oxygen you’d get at sea level by NASA’s model of the atmosphere. In 33,080 Apple Watch wearers, each kilometre of home elevation took about 1.2 points off a typical night and 0.8 off a typical day. Denver is 1.6 km up, so that’s about 1.9 points at night and 1.4 by day.
It’s like water boiling at a lower temperature in Denver. The stove is fine, and there’s just less air pressing down on the pot.
What’s typical for your age in Denver?
The range where about 95 in 100 watch wearers like you sit, with a BMI of 25, if the spread follows the usual bell curve:
| Age | Typical night average | Typical day |
|---|---|---|
| 25 | 92.3 to 97.1 | 93.5 to 98.0 |
| 40 | 91.6 to 96.5 | 93.1 to 97.5 |
| 45 | 91.4 to 96.3 | 92.9 to 97.4 |
| 65 | 90.6 to 95.4 | 92.3 to 96.8 |
These come from one watch model, the Series 6, in US wearers, and they describe a person’s usual nights, so one night can land outside them.
Your Denver 94 is a sea-level 96
Take an overnight average of 94 on an Apple Watch, for a 40-year-old. At sea level it sits at about the 5th percentile, low but still typical. In Denver the same 94 is right in the middle, about the 50th. Add back the 1.9 points Denver’s elevation takes off a night, and it’s about a 96 at sea level.
Awake, the lines don’t move much. MedlinePlus says levels may run lower if you live up high, and in the watch study a typical day at Denver’s height sat about 1.4 points lower. A new awake number of 92 or lower is still a reason to call your doctor.
What if you’re visiting?
Denver sits below the line where the CDC starts counting altitude risk, sleeping at 8,000 feet or higher. The ski towns are another story. In a study of 3,158 adult visitors to Colorado resorts between 6,300 and 9,700 feet, 25% got altitude sickness, most within 12 hours, and people who lived below 3,000 feet were 3.5 times as likely to get it. For a Colorado ski week from sea level, a night in Denver on the way up is the change the trip tool suggests (how to prevent it).
7 sources
- Shapiro I and others, Pulse oximetry values from 33,080 participants in the Apple Heart and Movement Study, npj Digital Medicine, 2023pmc.ncbi.nlm.nih.gov
- NASA Glenn Research Center, Earth atmosphere model, metric unitsgrc.nasa.gov
- HHMI BioInteractive, Partial pressure of oxygen: oxygen in the atmospheremedia.hhmi.org
- Merrick, Merrick helps measure Denver's fourth mile high marker, July 31, 2026merrick.com
- MedlinePlus, Pulse Oximetry, US National Library of Medicine, updated September 12, 2024medlineplus.gov
- CDC Yellow Book, High-Altitude Travel and Altitude Illness, updated April 23, 2025cdc.gov
- Honigman B and others, Acute mountain sickness in a general tourist population at moderate altitudes, Annals of Internal Medicine, 1993europepmc.org
