Hiking Water Calculator
Figure out how many liters and bottles of water to carry for a hike, adjusted for hot weather.
If you don't know your hiking hours yet, run the hiking time calculator first and use that estimate here. Your carrying capacity is the real limit on long days, so plan refills at water sources and carry a filter or purifier rather than trying to carry it all. Thirst lags behind dehydration, so drink on a schedule, not just when you feel thirsty, and add electrolytes once you're a couple of hours into hot-weather hiking.
How it works
The baseline is about 0.5 L of water per hour of moderate hiking. That number holds up reasonably well for a typical trail in mild conditions. Hot weather changes the math a lot, since you sweat more and lose water faster, so the calculator multiplies the baseline by 1.5 when you flag the hike as hot. Once you know the liters, it divides that by your bottle size and rounds up, since a partial bottle still counts as a bottle you have to carry.
Worked example: a 5 hour hike in mild weather needs 5 times 0.5, which is 2.5 L, or three 1 L bottles once you round up. The same 5 hour hike in hot weather would need 5 times 0.5 times 1.5, which is 3.75 L, noticeably more. A shorter 4 hour hike in hot weather needs 4 times 0.5 times 1.5, which comes out to 3 L even, or three 1 L bottles.
FAQ
What counts as "hot" for this calculator?
Anything meaningfully above a mild, comfortable hiking temperature, roughly 80°F (27°C) and up, or lower with high humidity or full sun exposure on an exposed trail. When in doubt, check the box and carry the extra water rather than guess low.
Can I really carry all the water I need on a long hike?
Not always. Water is heavy, about 1 kg per liter, so on long days your pack weight becomes the real constraint. That's why refilling at known water sources along the route, combined with a filter or chemical purifier, usually beats trying to carry a full day's supply from the trailhead.
Does this number include water for cooking or camp use?
No, this is drinking water for the hike itself. If you're also cooking at camp, washing dishes, or making coffee, add that separately, our camp stove fuel calculator assumes you already have the water on hand for boiling.
Why do I feel fine even when I'm already dehydrated?
Thirst is a lagging signal. Your body is often mildly dehydrated before you notice being thirsty, which is why drinking on a rough schedule (a few sips every 15 to 20 minutes) works better than waiting until you feel it.
For more on what to carry and how to plan around weather and water sources, see how to handle water and dishes at camp, the ten essentials every hiker should carry, and how to read the weather before a trip.