How heavy is your pack?

What the number tells you

A pack is a sum of four things that behave differently: the gear you own (base weight), and three consumables that you eat, drink and burn on the way. Splitting them shows where weight can come out. Base weight changes only when you buy or leave behind equipment. Food depends on days and effort. Water depends on the next source. Fuel depends on how you cook.

The method

The calculator multiplies each item's weight by its count and sums the list to get base weight. Food weight is the number of days times the weight of food per day. Water is liters times 1 kilogram per liter, which is 2.2 pounds per liter. Fuel is whatever you carry. The total is divided by your body weight to give the percentage. The base weight class is looked up from your base weight alone.

Worked example

A 150-pound hiker takes a 12.5-pound base, 3 days of food at 1.75 pounds a day, 1 liter of water and 4 ounces of fuel. Food is 5.3 lb, water 2.2 lb and fuel 0.3 lb, so the pack weighs 20.2 lb at the trailhead, or 13.5 percent of body weight. The 20 percent rule of thumb is 30 lb. Carrying 3 liters of water instead of 1 would bring the total to 24.6 lb, 16.4 percent. Base weight, 8 percent of body weight on its own, puts this hiker in the lightweight class.

What the guidelines say, and what they do not

The 20 percent rule is a rule of thumb repeated in retailer guides. We did not find a controlled study behind it, and it is easier for heavy hikers to meet than for light ones. The military figures come from loads that trained soldiers carry for work: the Army's field manual on foot marches (FM 21-18, 1990) sets a ceiling of 48 pounds for a fighting load and 72 pounds for an approach march, and military standard MIL-STD-1472F, as reported in a 2003 Marine Corps load report, recommends no more than 30 percent of body weight for close combat and 45 percent for marching. Those are limits for conditioned soldiers on a mission, not targets for a weekend hike. The manual itself says the question is how much a soldier can carry without impairing combat effectiveness, mentally or physically.

Common mistakes

• Using spec-sheet weights. A maker's number often leaves out stakes, stuff sacks or a footprint. Weigh each item on a kitchen scale and list it.
• Forgetting water and the second layer of food. Water is the heaviest item you carry on a dry route, and a bag of snacks adds up. Add them to the food-per-day figure.
• Comparing base weights between people. One hiker counts the clothes on their back, another does not; classes such as ultralight are labels from the backpacking community, with no standard body behind them.
• Treating the percentage as a pass mark. It ignores fitness, terrain, distance and how well the pack fits. See the rucking calories calculator for how a load changes the energy cost of walking.

Common questions

How much should my backpack weigh?

There is no law of nature and no single study behind one number. The figure most often repeated, including in retailer guides such as REI's, is about 20 percent of your body weight for a multi-day trip, which is 30 lb for a 150-pound hiker. Military research uses higher ceilings for trained soldiers, and your own back, knees and experience decide where you land.

What is base weight?

Base weight is the weight of everything in the pack except consumables: food, water and fuel. It is the number you control with gear choices, and it does not change from trip to trip. Some hikers also leave out clothing they wear; this calculator counts everything you list. Skin-out weight, the other common measure, adds everything you wear and carry.

What counts as ultralight?

By the usual convention in the backpacking community, a base weight under 10 pounds is ultralight and 10 to 20 pounds is lightweight. Sources disagree about where a conventional load starts (20, 25 or 30 pounds). These are labels people use, not standards; the calculator shows the label next to your base weight only as a reference.

How much does food weigh?

NOLS plans 1 to 1.5 pounds of food per person per day for short trips in mild weather, 1.75 to 2 pounds on a longer backpacking trip in cooler weather, and 2 to 2.5 pounds for cold weather and heavy packs. The camp food calculator turns those figures into a trip total. A 3-day trip at 1.75 pounds per day is 5.3 pounds of food for one person.

How heavy is water?

One liter of water weighs one kilogram, which is 2.2 pounds. Water is the largest swing in pack weight: carrying 3 liters instead of 1 adds 4.4 pounds. Carry only what the distance to the next source and the weather call for, and see the trail water calculator for the arithmetic.

Why does my pack get lighter during the trip?

Because food and fuel are consumed and water is drunk. The calculator shows the average daily loss from food and fuel. Water changes faster than that, so resupply points, not the day count, drive the heaviest day.

Does the percentage work for everyone?

Not equally. Percent of body weight is easy to compute but it favors heavier people: a 110-pound hiker with a 22-pound pack carries the same share as a 220-pound hiker with a 44-pound pack, and the first has a much smaller body to carry it with. Treat the percentage as a flag to check pack fit and training, not as a pass or fail.

This is a planning aid, not a safety assessment or medical advice. The percentages are rules of thumb. The right load depends on your fitness, health, the terrain and the weather.

Sources: Department of the Army, Field Manual 21-18, Foot Marches (1990), chapter 5, and MIL-STD-1472F, both as reported in the U.S. Marine Corps Combat Load Report (2003) and in G. King, "The Overweight Infantryman," Modern War Institute at West Point (January 10, 2017), the manuals themselves not opened here; REI, "How Much Should Your Pack Weigh?" (20 percent rule, as reported, page not opened); NOLS, "5 Steps to Plan a Camping Menu" (food per person per day); U.S. Geological Survey, Water Science School (1 liter of water weighs 1 kilogram). Base weight classes are community convention. Related: Camp Food Calculator, Trail Water Calculator, Rucking Calories Calculator, Hiking Time Calculator.