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If you're an average-healthy person from (near) sea level, how high may you climb a mountain before needing to stay at the altitude to acclimatise? Is it alright to go/drive up a 9000 ft (2750 m) mountain in one day or would it be dangerous?

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    @Chenmunka No, different people react differently. Some La Paz hotels apparently have oxygen bottles to assist the few guests who will feel ill, they do the same thing you did. Altitude sickness is nothing to take lightly. You don't need to be extra paranoid, but your comment is way too dismissive of the risks. Jul 25, 2023 at 22:37
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    Concerning Latin American places like Quito, La Paz or Bogota one has to make clear that they're within the tropics where the atmosphere is more stretched-out so that those cities are barometrically lower than they actually are. While Quito is at 9300 ft above sea level, a plane's altimeter calibrated to 29.92 would likely show something like 8000 ft at Quito's altitude. Mt Shasta, Mt Hood and Mt Rainier are on the midlatitudes so their absolute altitude should match the pressure altitude approximately. Denali otoh is so far north that it's barometrically higher than it actually is.
    – Johannes
    Jul 26, 2023 at 5:20
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    @Johannes Another important point is that if you fly to a high altitude airport, you are effectively acclimatizing onboard the airplane. The cabin is pressurized to about 75 - 85 kPa (about 2500 - 1700 m altitude). I tend to get a headache when taking a cable car to 2500 metres in Europe, but I observed no ill effects after flying to Chile and driving to 3400 m straight from the airport. Jul 26, 2023 at 11:10
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    @Martin'Kvík'Baláž The maximum allowed cabin altitude of a plane is indeed 8000 ft (2440 m), but modern planes don't reach such cabin altitude anymore and any plane usually has a much lower one, around 4000-6000 ft (1200-1830 m) at cruise altitude. You'd need to fly in an old plane at FL400 or so to experience 8000 ft onboard a plane.
    – Johannes
    Jul 26, 2023 at 11:16
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    @Johannes Yes. I carry a Garmin with me on all flights. Unfortunately the pressure data are not stored in the GPX file, but if memory serves, LATAM and BA A320s and Iberia A340s were pressurized to about 75 kPa, newer BA Dreamliners and Air France A220s indeed to 85 kPa. But for us living almost at sea level it could help anyway. Jul 26, 2023 at 21:02

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People react differently to altitude, and it is not always those you would predict who have trouble at altitude. Thus, my advice is to take it slower than zero to 9,000 feet in one day unless you have done it before with no problems.

Driving up to 9,000 feet is one thing, because you can quickly retreat. Hiking up, especially if you spend the night, is more problematic. Moreover, hiking up 9,000 feet in one day, especially with a pack, unless you have done it before, is probably not the best plan, independent of the altitude.

Consider that the guided hikes up Rainier, for example, which have a 9,000 foot elevation change (5,400 feet to 14,400 feet), do it in two days. Do you want to drive up to Paradise Inn (5,400 feet) from sea level and immediately hike up to Camp Muir (10,000 feet) (which is a non-technical, easy hike)? My advice, based on personal experience, and the level of familiarity with altitude that your question suggests is "no".

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    Drive+hike (options other than driving may be available) is a realistic way to get towards a worst-case risk, and something to beware of as Exercise exacerbates AMS
    – Chris H
    Jul 26, 2023 at 8:46
  • I was told that there are three stages to altitude sickness. Stage 1 - Acute Mountain Sickness resembles a hangover. Stage 2 - cerbral anema resembles an alcohol intoxication. Stage 3 - Pulmonary edema resembles drowning due to fluid in your lungs. Don't take my word as medical advice, but stage 2 and 3 if untreated will probably kill you. Luckily rare below 14000 feet of elevation.
    – ghellquist
    Jul 27, 2023 at 8:57
  • @ghellquist, your "stages 2 and 3" aren't stages, they're parallel sets of effects, and you can get one without the other. They'll both kill you, though cerebral edema will kill you faster, and you can usually self-rescue if you recognize that you're suffering pulmonary edema.
    – Mark
    Jul 27, 2023 at 19:12
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As a rule of thumb, high altitude sickness can start at around 2500m. However, for most people this will not be serious yet (maybe except for getting out of breath quickly), especially when only there for a short time. Otherwise, skiing, hiking and driving mountain passes would be a lot more problematic.
For most people, problems start when they stay overnight at around 3000m. Keep in mind that things start to change quickly when you go further up. The step between 2500m and 3000m might be the same altitude difference as going from 3000m to 3500m, but the effect is vastly different.

Given that the symptoms are mild at medium altitudes and the body will adapt quickly, the best way is to try things out and see how you feel. If you go higher than 3500m - especially overnight - I would recommend some acclimatization beforehand. Above those altitudes, it is recommended to limit your sleeping altitude to an increase of around 500 vertical meters per day and plan for sufficient rest days

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    I'm not sure altitude-related breathlessness on exertion should even be considered a symptom of AMS, at least not in isolation. It's just effect of getting about 25% less O₂ per breath than at sea level. Look out for proper symptoms and treat accordingly
    – Chris H
    Jul 26, 2023 at 8:52
  • "limit your sleeping altitude to an increase of around 500 vertical meters per day" how do you go skiing for a week when you live at ~0m and the chalet is at 1500-2000m?
    – njzk2
    Jul 26, 2023 at 17:14
  • @ChrisH In hospital, 75% spO2 would mean you need to be put on supplemental oxygen, so I don’t get why you’re treating it as not serious. Jul 26, 2023 at 19:06
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    @PlaceReporter99 because 75% pp O₂ in the air doesn't mean 75% spO₂ in the blood. They're completely different.
    – Chris H
    Jul 26, 2023 at 20:15
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    @njzk2 This is increase is referring to the altitude above the critical level. So, if you are Dutch and going skiing, there is no problem. But if you want to spend a night at Capanna Margherita, you probably should spend some nights at high altitude beforehand
    – Manziel
    Jul 27, 2023 at 6:14
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The highest places for mass tourism in Switzerland are Jungfraujoch (3466m / 11370ft) and Titlis (3238m / 10620ft). People from all over the world - in particular from far-eastern countries - go there in just one day, with their hotels at maybe 400m. If people would regularly get health problems or pass out during that trip, those trips wouldn't be so famous and crowded.

All the tourists descend at the same day though (there's no public accomodation there) and they're not supposed to hike or do other intense activities there, so this might also reduce the impact. And the railway up to Jungfraujoch makes two short stops during ascent - officially to offer a great view from a station in a cave, but in fact to acclimatise the passengers.

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  • That's wild. As a kid I went on that train (to Jungfraujoch), and I remember the stops. I had no idea how high it was. Jul 26, 2023 at 18:00
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    Precisely. IMO concern for altitude sickness for lower elevations is overblown, exaggerated. When things get close to 4000m or more then it becomes important. There are many mountain huts in 2500+ range. Here mass of tourists go to 2864m mountain and then sleep in a hut at 2500+ m high from low elevation. I don't know about any altitude sickness problems. Nobody doesn't talk about that. The problems are lack of experiences with mountains and people go up in bad weather - lightning strikes, that is more pressing issue and more dangerous.
    – Alex J.
    Jul 26, 2023 at 21:32
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As airplane usually climbs from sea level to many thousands feet within minutes, while maintaining cabin air pressure at 8,000 feet throughout, I would say a sudden climb to 8,000 feet is perfectly safe.

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    A sudden climb to 8000 feet is perfectly safe for most people, particularly when coupled with a sudden descent back to acclimatization altitude a few hours later. A sudden climb to 8000 feet and then staying there overnight produces a few dozen emergency medivacs from Yellowstone National Park every year.
    – Mark
    Jul 27, 2023 at 19:16
  • @Mark are those medivacs due to altitude sickness though? A lot of things can go wrong on the mountain. Jul 28, 2023 at 16:07
  • @JonathanReez, that's just the altitude-sickness medivacs. The other common reasons for medivac from Yellowstone are heart attacks, strokes, and injuries from car crashes. Medivac for wilderness-related reasons (falls, animal attacks, burns from thermal features, etc.) are relatively uncommon.
    – Mark
    Jul 28, 2023 at 18:26
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    @Mark do you have the link to the stats? It seems bizarre that so many people get medevaced from an elevation of 8000 feet due to altitude sickness alone. Jul 28, 2023 at 18:43
  • @JonathanReez, no link, I got the numbers from talking to a ranger. Keep in mind that Yellowstone gets about three million visitors a year, most of them lowlanders.
    – Mark
    Jul 28, 2023 at 21:42
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In Colorado, you can drive to almost the top of Mt Evans. There is a parking lot about 100 feet feet below the 14,271 ft (4,350m) peak. I have been there repeatedly and have taken a number of my relatives. There are taller mountains than this in Colorado, but this is the highest road.

One of the most noticeable things, and the reason I have taken my relatives up, is that I got noticeably dizzy as soon as I got out of my car and stood up. That's actually one of the tourist attractions -- noticeable altitude sickness. It was enough to feel, but not enough to stop me from actually doing anything. I'm not in the best shape, and the remaining 1/4 mile (400m) trail to climb the remaining ~100ft of elevation to the top is pretty steep, but I was still able to make it up to the top.

Some of the relatives that I took up there flew from near sea-level to Denver (5280ft/1600m) and went with me the rest of the way up the next day.

Based on this experience, I think that at least 15000 feet is not an issue. This covers the entire 48 contiguous United States, and something like 99% of the entire Earth.

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  • the reason I have taken my relatives up, is that I got noticeably dizzy as soon as I got out of my car and stood up. and you wanted them to experience this too? 🤪
    – Andy
    Jul 27, 2023 at 17:22
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    Always iffy to generalize from one's own experience to what is advisable for most people. I wrote a very cautious answer to the Q, because the OP seemed to have little (or maybe no) experience at even moderate altitude. The neophyte should cautiously find out how altitude affects her or him. As for being passively transported to over 14,000 (your Mt. Evans example), or getting on a plane, this is very different from hiking up and/or staying overnight.
    – ab2
    Jul 27, 2023 at 21:09
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    Getting dizzy like that isn't altitude sickness. Jul 28, 2023 at 2:40
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You're asking a question that doesn't have a real answer because it depends on the person.

I have driven 5,000' to 12,000' without any issue. I have drive + hike from 3,500' to 12,000' without problems. I have drive + hike from 3,500' to 10,000'+ many times, no problems. I have hiked 5,000' to 18,000' over thee and a half days, no problems--even though nearly 80% of our group had to turn back at 15,500'.

I would hesitate to drive my wife from 5,000' to 12,000', though, and would keep an eye out for symptoms and head down immediately if it were an issue.

I would not even consider driving her sister from 5,000' to 12,000'.

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I often go from 300 m height to 2500 - 2800 m in a day, sometimes I sleep at 2500 - 2700m without any problems. I think there is enough oxygen, pressure high enough and if you are average health you shouldn't be concerned.

In my country people often go from low elevation to 2800m in a day and I don't see anyone making complains or talking about acclimatization.

If you would go above 3000 - 3900 m then yes you should acclimatize for a day.

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    If in your country it is common to go to that elevation isn't it that most people are kind of acclimatisized in a way that people with no mountains in their country are not? The highest point in my country is all of 300 meter.
    – Willeke
    Jul 25, 2023 at 22:28
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    @Willeke Agree. When we lived in Berkeley (sea level) we would drive to Yosemite on Friday for the weekend at least twice a month. We'd drive to trailheads at 7,000 feet to 9,000 feet, and then hike up another 500 feet or so to isolated camping places. We were almost permanently acclimitized to these altitudes. That changed when we moved back east.
    – ab2
    Jul 25, 2023 at 23:08
  • Most people live in 200-400m elevation and don't go to mountains all the time, so they are not acclimatized. Tourists and natives go from low elevation to 2800m, sleep at 2500m and they don't have problems. Tiny shortness of breath is not dangerous if someone gets that. The danger in that elevation is not "acclimatization." It is lack of experience, equipment, going to too demanding mountains or in bad weather, when there is thunderstorm development. That is the danger. Not acclimatization.
    – Alex J.
    Jul 29, 2023 at 12:40
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It's almost less about being at a certain altitude than exerting yourself at a particular altitude. And it depends on the person. If you're just driving up to 9000ft, can't imagine it making a huge difference, unless you're sensitive.

Climbing a mountain is a different matter. I lived in Vail for years (8250 feet, with area peaks going over 13,000ft). I remember going for a run my first week there, and realizing there would be an adjustment period. That's when I noticed. It wasn't just being there, or taking slow and steady walks, it was exerting myself. I was out of breath to the point it hurt to breathe in less than a mile (about a half km). Even after living there for years and fully acclimating, while regularly being active, the altitude has an effect. You notice, when you're tired and panting, there is less oxygen getting to your body. Recovery can also take longer, at least if you're not used to it. My first climb in Vail, I had to take the whole next day to rest as my legs were just shot.

So, if you're climbing a mountain... depends on you. I hear of people going from sea level to Colorado just for a weekend to run an ultramarathon, and some of those people report no ill effects (though they are clearly in excellent physical shape to do this, and have been training for the extreme lengths of running at sea level, still). Someone else doing that could pass out after a few miles. In Denver, at about 5200ft, I never really noticed much. So, I'd say somewhere around the 7000ft mark is where you may start to feel it more, on a guess.

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