Altitude Hydration Calculator

At high altitude, your body loses water much faster than at sea level.
The air is drier, you breathe faster, and your body works harder to acclimatize.

Why altitude increases water needs:

• Lower humidity: Air above 5,000 feet (1,500 m) is significantly drier. You lose more moisture through breathing and skin evaporation.
• Increased respiration: Your body breathes faster and deeper to compensate for lower oxygen, exhaling more water vapor.
• Increased urination: The body produces more urine at altitude as part of acclimatization.

General hydration guidelines by altitude:

• Sea level to 5,000 ft (1,500 m): Normal intake, about 2-3 liters per day
• 5,000-8,000 ft (1,500-2,400 m): Add 0.5-1 liter per day
• 8,000-12,000 ft (2,400-3,600 m): Add 1-1.5 liters per day
• Above 12,000 ft (3,600 m): Add 1.5-2+ liters per day

These additions are planning figures, not published values. No mountain-medicine body sets an exact amount per altitude band, which is why the urine-colour check further down matters more than the total.

Activity level matters significantly.

Hiking or skiing at altitude can require 4-6 liters per day or more.
Even light walking increases needs compared to resting.

Temperature also plays a role.

Cold, dry air at altitude causes additional moisture loss.
Hot conditions at altitude combine both heat and altitude dehydration effects.

Signs of dehydration at altitude include headache, dizziness, dark urine, and fatigue.
They overlap with altitude sickness, but water is not the cure for that. Drinking extra has not been shown to prevent altitude sickness, and overdrinking adds the risk of low blood sodium. What prevents it is a slow ascent: above 3,000 m (about 9,800 ft), the Wilderness Medical Society advises sleeping no more than 500 m higher each night, with a rest day for every 1,000 m gained.

Tip: Drink before you feel thirsty. By the time you feel thirst at altitude, you may already be dehydrated.

Water alone is not the whole answer past about 5 liters a day.

Sweat carries sodium out with the water, and at altitude the diuresis of acclimatisation takes more salt with it. Replacing the volume with plain water and nothing else dilutes blood sodium, which produces exactly the headache and nausea you were trying to avoid. Guides on Rainier and Kilimanjaro push electrolyte tabs for this reason, not as an upsell.

There is also a ceiling, and it is hourly. The kidneys clear roughly 0.8 to 1 liter an hour at best, so the danger is drinking faster than that, whatever the daily total. If the number below comes out at 10 liters or more, treat it as a sign that the activity level is extreme rather than as a target to hit.