How Heavy Should a Backpack Be? The 20% Guideline
Overpacking is one of the most common ways a trip goes wrong before it starts. A pack that is too heavy slows you down, makes every climb harder, puts more load through your knees on every descent and makes a stumble on rough ground more likely to become a fall. The usual question is "how heavy is too heavy?", and the usual answer is a rule of thumb: keep a loaded pack at or under about 20% of your body weight.
The Backpack Weight Calculator applies that guideline. This guide shows how, works one pack through three hikers of different sizes, and is clear about what the 20% figure is and is not.
What the calculator adds up
It splits the load into two parts, the way backpackers usually talk about it:
- Base weight: everything that stays the same through the trip. The pack itself, shelter, sleeping bag and mat, stove and pot, clothing you carry but are not wearing, first aid, navigation, headlamp.
- Consumables: food, water and fuel, which get lighter as you go.
Total pack weight is base plus consumables. The calculator divides the total by your body weight to get a percentage, says whether it is within the 20% guideline, and classes the base weight as ultralight (under 4.5 kg), lightweight (under 9 kg) or traditional (9 kg or more).
One pack, three hikers
Take a hypothetical overnight pack: 9 kg base weight, 2 kg of food, 3 litres of water (3 kg) and 0.3 kg of fuel. That is 5.3 kg of consumables and a 14.3 kg total, with a base weight right on the line into the traditional class.
| Hiker's body weight | Pack as % of body weight | Within 20%? |
|---|---|---|
| 60 kg | 23.83% | No |
| 70 kg | 20.43% | No, just over |
| 85 kg | 16.82% | Yes |
Identical gear, three different answers. That is the point of a body-weight guideline: a pack that is comfortable for a larger hiker can be a real burden for a smaller one. Couples and groups who split shared gear evenly by item, rather than by what each person can carry, often end up with the smallest person carrying the largest share of their own body weight.
Getting the 60 kg hiker under the line
For the 60 kg hiker, the pack is almost four percentage points over the line. There are two places to look.
Reduce the base weight. If the 9 kg base comes down to 5.5 kg, perhaps with a lighter shelter, a lighter sleeping bag and a smaller pack, the total falls to 10.8 kg, which is 18% of body weight and within the guideline. The base weight also moves from traditional to lightweight. Base weight is where lasting savings come from, because you carry it every day of every trip.
Reduce the consumables. If the route has reliable, confirmed water sources and the hiker carries 1.5 litres instead of 3, the total falls to 12.8 kg, which is 21.33%: better, but still over. Cutting water only works when the water is genuinely there to refill, and cutting it too far is dangerous in heat. See carrying water versus filtering it.
The example shows a general pattern. Consumables are the obvious target because they are heavy and flexible, but the safe amount of food and water is set by the trip, not by the pack. Base weight is the part you can change without making the trip less safe, provided the essentials stay.
What the 20% guideline is, and is not
The 20% figure is a rough guide that comes from backpacking practice. It is useful for a quick check, and the calculator flags when you cross it so you can decide what to leave behind. It is not a medical recommendation, and it is not a safe limit in either direction:
- It is an adult rule of thumb. It is not a figure for children. For children's backpacks, the American Academy of Pediatrics' HealthyChildren.org advises no more than 15% of the child's body weight; if you are planning a trip with children, keep their loads light and ask your child's doctor if you have concerns.
- Under 20% is not automatically comfortable. Someone with a back, hip or knee problem, or someone new to carrying a pack, may struggle well below it.
- Over 20% is not automatically dangerous for a fit, experienced hiker on a short trip. But each extra kilogram costs more than the last, and the risk of strain and falls rises.
- It ignores the route. Twenty per cent on a flat forest path and twenty per cent on a steep, rocky climb are very different days.
- It is about the pack you start with. Food and water are heaviest on the first day, often on the first climb.
If you have a medical condition or an injury, the guideline does not replace advice from a doctor or physiotherapist.
Weight is not only about comfort
A heavier pack also changes the other numbers in your plan. It slows you down: the Hiking Time Calculator's "leisurely / heavy pack" setting adds 25% to the time estimate, which in turn moves your turnaround time and your water needs. And it costs energy: the Hiking Calorie Burn Calculator shows each extra 5 kg costing more than the last; see whether a heavier pack burns more calories.
Weighing your pack properly
- Weigh everything once. A kitchen scale for small items and a luggage or bathroom scale for the big ones. Write the list down; the base weight number is then a fact rather than a guess.
- Weigh the packed pack. Stand on a bathroom scale with and without it. The difference is the real total, including the things you forgot to list.
- Count water as weight. A litre of water weighs about a kilogram.
- Do not count what you wear, but do count spare clothing in the pack.
Do not cut the safety margin
The easiest kilograms to lose are often the ones you need on a bad day. Whatever the calculator says, keep the ten essentials: navigation, a headlamp, sun protection, first aid, a knife or repair kit, a way to make fire where permitted, an emergency shelter, extra food, extra water and a way to treat more, and extra clothing. Our guide to what the ten essentials weigh shows they add surprisingly little. Trim luxuries, duplicates and over-packed food first.
Then fit the pack properly, with the hip belt carrying most of the load, and try it on a shorter walk before a big trip. A well-fitted pack under the guideline, with the essentials in it, is the goal. The number is just how you check you have got there.