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If I know my route will take x days, over terrain y, with a change in height of z, in temperatures of p, is there a simple rule of thumb which will let me calculate food requirements?
Water is relatively easy, but I always find myself erring on the side of too much food in my rucksack.
2000 calories is the "standard" daily diet amount, so I usually shoot for 3000 calories per day plus 1 to 3 extra days, in case I get delayed or distracted and want or need to stay out longer. And I usually pack out some food.
You can get a rough estimate from using an online calorie estimation website. Make sure to use one that accepts weight as a variable, and add your pack weight to your body weight. I am a large guy, and would burn over 4000 calories a day hiking for 6 hours with a pack. Most calculations aren't going to take specifics like change in elevation, or temperature.
There is no simple algorithm to calculate calory needs. It depends on many conditions, such as the intensity of the trek, the temperature and humidity, your metabolism, what you are wearing etc.
My typical calory usage (70kg weight) in mountains measured in Crna Gora in August, route between 20 and 30 GOTs (1 GOT is 1 km distance or 100 m elevation) was between 4500 and 6000 kcal. A woman, 50kg, has in the same time calory usage between 3000 and 3500 kcal.
My collegue is writing a doctor thesis based on such measurements, and I will encourage her to publish the results. But the amounts above are, according to her, typical.
