Loading page
About this tool
Hour-by-hour drinking plan for a flight, accounting for dry cabin air, alcohol and caffeine, plus arrival time and jet lag.
The Flight Hydration Planner turns flight length, cabin conditions and what you drink on board into an hourly millilitre target, and works out your arrival local time and caffeine cutoff at the same time. Aircraft cabins are pressurised to a cabin altitude of up to 8,000 feet with relative humidity typically between 10% and 20%, and the extra water that costs you is computed here from psychrometrics rather than assumed. The usual finding surprises people: on a ten-hour flight the dry air costs roughly 50 ml, while two beers cost about 260 ml in extra urine.
Open Flight Hydration Planner on AltFTool — it loads instantly in your browser.
Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
Shows the dry-air loss as a real number rather than repeating the claim that flying badly dehydrates you.
Converts each drink to grams of ethanol from its volume and ABV, then applies the roughly 10 ml of urine per gram effect.
Gives arrival local time, day rollover, zones crossed and a caffeine cutoff six hours before your destination bedtime.
A common airline recommendation is around 250 ml an hour, and this planner usually lands near that for a long-haul once alcohol is included. For a 70 kg adult on a ten-hour flight with two beers and a coffee, the total works out around 1.5 litres, or roughly three 500 ml bottles.
Far less than the folklore suggests. Cabin humidity of 10-20% adds only about 50 ml of extra water loss over ten hours through breathing and the skin, because exhaled air is saturated at body temperature whatever you inhaled. The dry eyes, blocked nose and scratchy throat are real, but they come from surface evaporation on those tissues, not whole-body fluid loss.
Ethanol suppresses vasopressin, the hormone that tells the kidneys to conserve water, producing roughly 10 ml of extra urine per gram of ethanol consumed. A 330 ml beer at 5% contains about 13 grams, so two beers cost around 260 ml — about five times what ten hours of cabin air costs. Alcohol also fragments sleep, which compounds jet lag.
About six hours before the bedtime you intend to keep at your destination. Caffeine has a mean elimination half-life near five hours, and controlled trials show a dose taken six hours before bed still measurably reduces total sleep time. Shifting your caffeine to the destination's morning is one of the more effective jet-lag habits; recovery otherwise runs at roughly one day per time zone crossed.