Water Carry Calculator (How Much Water to Carry)

Water is the heaviest thing most hikers carry and the only thing they can refill for free. At 2.2 lb per litre, filling four litres out of habit puts more weight on your back than an entire ultralight base weight. This calculator estimates how much you need for the stretch ahead based on distance, pace, heat and terrain, and tells you what that water weighs before you commit to hauling it uphill.

What does water actually weigh?

One litre of water weighs 2.2 lb, which is 35.3 ounces or 1 kilogram, and one US gallon weighs 8.34 lb. Those numbers are the reason water dominates pack weight decisions: no gear purchase available to you moves weight as fast as choosing to carry one litre instead of three.

The comparison column is the useful part. Somebody agonising over a 6 ounce difference between two rain jackets is looking at a decision worth less than a fifth of a litre. The same person topping off to four litres at every creek is carrying the equivalent of a second gear list. The full conversion table sits on the water weight chart.

How much do you drink per hour?

The working anchors are about 0.5 litres per hour of walking in mild conditions and up to 1 litre per hour in heat or on sustained climbing. Everything else is a modifier on those two. Full sun with no shade pushes you toward the top of the band, as does altitude, because you lose water breathing dry air faster than you notice.

Then add the fixed costs. Cooking at the far end is about 1 litre once you include a hot drink and rinsing a pot. A dry camp is another litre for the evening and the first part of the morning. Those two additions are why a modest 3 hour stretch can turn into a 3.5 litre carry even in good conditions, and why campsite choice moves more water weight than pace does.

Individual variation here is genuinely large. Sweat rates differ by more than a factor of two between people of similar size doing identical work, so use your own experience over any table once you have some. The calculator rounds up to the nearest half litre on purpose.

When should you carry more rather than filter more?

Carry big in four situations: the next source is seasonal rather than reliable, the stretch is long and exposed, you are camping dry, or you are moving through country where a failed source leaves you with no alternative for hours. That covers most of the desert, much of the Sierra late in a dry year, and a lot of ridge walking.

Filter more in everything else. In terrain where you cross water every few miles, carrying two litres all day is 4.4 lb of self-inflicted training. The kit that supports drinking little and often is a fast filter you can use without unpacking, plus one bottle you can reach on the move, which is the argument made in full in the water treatment guide. Desert planning is a different discipline entirely, and the desert gear list assumes long dry stretches from the start.

What can go wrong with the treatment itself?

Two failure modes matter more than the rest, and neither shows up in a weight column.

First, hollow fibre filters are destroyed by a single freeze, with no visible sign of damage. The fibres crack, the filter still flows, and it is no longer filtering anything. If overnight temperatures are near freezing, sleep with the filter inside your quilt and keep it there. A filter that has frozen, or that you suspect has frozen, gets replaced rather than tested.

Second, filters remove bacteria and protozoa but not viruses. At 0.1 micron they handle giardia and cryptosporidium, which is what most North American backcountry water presents, and a virus risk means chemical treatment or a purifier instead. The practical answer for almost everyone is a filter plus a few chlorine dioxide tablets as a backup, which weighs under an ounce and covers the clog, freeze and split failures. The trade-offs between the two methods are compared in filter versus chemical treatment, and the current picks are in the water filter roundup.

Water treatment is never a place to save weight. Going ultralight must not mean going unprepared, and a treatment plan with no backup is one clogged cartridge away from a decision nobody wants to make at the end of a long dry day.