About this tool
Hiking Water Calculator is a free, in-browser tool that estimates how much water to pack for a hike so you neither run dry nor haul unnecessary weight. Enter the expected duration, choose the conditions from cool to hot, and add your elevation gain, and it returns the recommended water in liters, fluid ounces and bottle counts. Everything is computed locally; nothing is uploaded.
The estimate starts from a baseline of about 0.5 liters per hour of walking and adds a heat and exertion allowance of 0.1 to 0.3 L per hour for warmer or more strenuous conditions. Climbing burns extra fluid, so it adds roughly 0.1 L for every 300 m of ascent, then applies a 15% safety buffer for hotter-than-expected days, spills and unplanned delays. The result is shown as liters, ounces, and the number of 500 mL bottles and 1-liter Nalgene-style bottles to carry.
Treat the figure as a planning minimum and always know where you can refill or filter on longer routes. Drinking to thirst is a good guide, but in heat or at altitude your needs rise sharply — pair the water with electrolytes on trips over two hours or in hot weather to replace the salts lost through sweat.