How we calculate it
First we estimate the calories your body burns at rest (your basal metabolic rate) with the Mifflin–St Jeor equation, from your weight, age and sex. We assume an average height: 5 ft 9 in for men and 5 ft 4 in for women.
Then we multiply that by an activity factor for the trip: 1.8 for easy, 2.1 for moderate, 2.5 for hard and 3 for extreme. Finally, we turn calories into food weight by dividing by how calorie-dense your food is.
The detailed estimate
Choose “Add trip details” and the activity factor is replaced by what a typical day actually asks of you. Resting and camp life come to 1.3 times your basal rate. Walking adds about 0.5 calories per kilogram of you plus your pack for every kilometer. Climbing adds the work of lifting that weight uphill, at the 22% efficiency of human muscle. Going downhill is counted as free.
Terrain scales the cost of walking and climbing using the terrain factors the US Army uses for load carriage (Soule and Goldman, 1972): 1.0 for pavement, 1.1 for a dirt trail, 1.5 for bushwhacking, 2.1 for loose sand and 2.5 for soft snow. Cold adds 8%, heat 4%, and altitude 5% above 8,000 feet or 10% above 12,000. Those last three are rules of thumb. Walking, climbing and terrain are standard exercise physiology, and we checked that the typical trips line up with the simple estimate within about 10%.
We don't ask for your pace. Walking a mile costs about the same whether it takes 20 minutes or 30. Distance, climbing and pack weight are what move the number.
How many calories do backpackers need per day?
For the hikers below, it ranges from about 2,300 to 5,600 calories a day. Bigger bodies and harder days burn more.
| 30 years old | Easy | Moderate | Hard | Extreme |
|---|---|---|---|---|
| 130 lb woman | 2,335 | 2,725 | 3,244 | 3,892 |
| 160 lb woman | 2,580 | 3,010 | 3,584 | 4,300 |
| 160 lb man | 3,014 | 3,516 | 4,186 | 5,023 |
| 200 lb man | 3,341 | 3,897 | 4,640 | 5,568 |
How much does that food weigh?
It depends on calorie density, the calories in each ounce of food. Some rough figures:
- Olive oil: about 250 calories per ounce
- Nuts and nut butters: roughly 160 to 200
- Chocolate: around 150
- Freeze-dried meals: often 100 to 140
- Fresh fruit and vegetables: under 20
A mix that averages 120 calories per ounce works out to roughly 2 pounds of food per person per day on a hard trip.
Treat it as a starting point
Cold weather, altitude and heavy packs all push your needs up. On longer trips, most people get much hungrier after the first week or so (“hiker hunger”), so plan for bigger resupplies later on. If you're losing weight fast, eat more.