Hiking water calculator
How much water should you carry? Enter how long you will be out, how warm it will be and how hard the walking is. You get a per-hour figure, the total, and the formula behind it.
Carry about3.2 L107 US fl oz, weighing 3.2 kg (7.0 lb)
- Drink per hour
- 0.59 L
- Expected to drink
- 2.7 L
- Spare on top
- 0.5 L
- Every 20 minutes
- about 200 ml
0.50 L/h for mild weather + 0.09 L/h for 22 °C = 0.59 L/h
- This is an estimate. Sweat rates vary a lot between people: carry more than you think you need, and drink before you feel thirsty.
How the estimate works
Hiking guides commonly suggest about 0.5 L per hour in moderate weather. On a hot day, the US National Park Service at Shenandoah says the average hiker drinks about a quart (0.95 L) an hour, in line with NIOSH's advice of ¾ to 1 quart an hour for work in the heat. We use 0.5 L/h up to 20 °C (68 °F), 0.95 L/h from 30 °C (86 °F), and a straight line between, which is our own simplification. Hard walking adds 0.25 L/h (about half a litre more per two hours), and at altitude or in hot, dry air we use at least 1 L/h. We never suggest drinking more than 1.4 L (48 fl oz) an hour, NIOSH's upper limit.
Your own sweat rate is better
People sweat at very different rates, so the American College of Sports Medicine suggests estimating yours by weighing yourself before and after exercise: every kilogram lost is about a litre of sweat, plus whatever you drank. Its goal is to avoid losing more than 2% of body weight. In the heat, Grand Canyon rangers warn that hikers can lose one to two litres an hour, more than you can drink, so also slow down, rest in shade and eat salty snacks.
Sources
- Vancouver Trails. How much water should I bring?
- Advnture. Water for hiking: how much do you need to carry?
- US National Park Service, Shenandoah. Drinking water.
- NIOSH. Heat stress: hydration. DHHS (NIOSH) Publication 2017-126.
- Backpacker. How to stay hydrated and treat dehydration.
- American College of Sports Medicine; Sawka MN, Burke LM, Eichner ER, et al. Exercise and fluid replacement. Medicine & Science in Sports & Exercise 2007;39(2):377–390. doi:10.1249/mss.0b013e31802ca597
- US National Park Service, Grand Canyon. Hike smart.
Questions
Can I drink too much?
Yes. Drinking far more than you sweat, without food or salt, can dilute the sodium in your blood, which is dangerous. Eat as you go, add electrolytes on long hot days, and stay under the hourly limit shown here.
Should I carry less if there are streams?
You can carry less between reliable sources, if you treat the water. Enter the longest stretch between refills; the reserve still applies, because springs can run dry.
Does cold weather mean less water?
We do not go below 0.5 L an hour. Sweating under warm layers still costs water, so the baseline stays the same however cold it is.