Hiking Water Needs Calculator
Work out how much water to pack from the hours you’ll be out, the temperature, and how hard you’ll be working — with a nudge on when to add electrolytes.
Enough water, without the dead weight
Water is the single heaviest thing most hikers carry, and getting the amount wrong hurts either way — too little risks dehydration, too much is dead weight up every climb. Matching the amount to the day’s length, heat, and effort lets you carry what you need and no more.
See how much those litres add to your load with the Backpack Weight Calculator, and estimate the effort that drives your thirst with the Hiking Calorie Burn Calculator.
Frequently Asked Questions
How much water should I carry per hour of hiking?
A widely used field baseline is about half a litre of water per hour of moderate hiking, rising well above a litre an hour in heat or on hard climbs. This calculator starts from that baseline and scales it by temperature and exertion, so a cool, easy stroll and a hot, steep slog give very different totals. It is a planning figure — your real need depends on your body, the humidity, and how much you sweat.
Why do temperature and effort change the number so much?
Your body sheds heat mainly by sweating, and both a hot day and a hard effort raise how much heat you produce. That means fluid loss climbs steeply as the mercury rises and as the trail steepens under a heavy pack. Because both stack, a long, hot, strenuous day can call for two or three times the water of a cool, gentle one of the same length.
When do I need electrolytes rather than plain water?
Sweat carries salt as well as water, and on long, hot, strenuous outings replacing water alone can dilute your sodium and leave you feeling worse. The tool flags when conditions — several hours, high heat, and hard effort — make electrolyte drinks or tablets worth carrying. For shorter or cooler hikes, plain water and normal trail snacks are usually enough.
Should I carry all my water or plan to refill?
Water is heavy — roughly a kilogram per litre — so on long routes many hikers carry less and refill from reliable sources, always filtering or treating first. Check your map and current conditions for springs, streams, and caches before deciding, and use the backpack weight calculator to see how much the water you plan to carry adds to your load.
Planning guidance only, not medical advice. Drink to thirst, watch for signs of dehydration, and always carry a margin plus a way to filter or treat more water.