Hiking Hydration Calculator
Enter your weight, how long you will be out and the conditions. You get how much to drink per hour, the total for the hike, and when it is worth planning refills.
Someone shared this result with you. Change any value to run your own numbers.
Water to carry- Per hour
- Bottles
- Water weight
How the Hydration Calculator Works
The calculator works per hour, the way you drink on the trail: it finds how much water an hour of hiking takes in your conditions, then multiplies by the hours you will be out. Every number it uses is in the tables below, so you can check any result by hand.
1. Water per hour, by temperature and effort
Start from the air temperature you expect and how hard you will hike. Easy is flat and relaxed, moderate is rolling and steady, strenuous is steep or fast.
| Air temperature | Easy | Moderate | Strenuous |
|---|---|---|---|
| Below 50°FBelow 10°C | 10 oz0.30 L | 14 oz0.40 L | 19 oz0.55 L |
| 50 to 67°F10 to 19°C | 12 oz0.35 L | 17 oz0.50 L | 22 oz0.65 L |
| 68 to 76°F20 to 24°C | 15 oz0.45 L | 20 oz0.60 L | 25 oz0.75 L |
| 77 to 85°F25 to 29°C | 17 oz0.50 L | 24 oz0.70 L | 29 oz0.85 L |
| 86 to 94°F30 to 34°C | 24 oz0.70 L | 29 oz0.85 L | 34 oz1.00 L |
| 95°F and up35°C and up | 32 oz0.95 L | 36 oz1.05 L | 41 oz1.20 L |
The moderate column at 50 to 67°F10 to 19°C matches the common rule of about 17 ozhalf a liter an hour of moderate hiking in moderate temperatures. The hot rows follow the US Army heat guide, which asks for about 16 to 32 oz0.5 to 1 liter an hour depending on heat and workload.
2. Sun exposure
Full sun adds water and shade saves some, but mainly once it is warm. The Army guide puts the swing at about a quarter quart an hour between full shade and full sun.
| Air temperature | Mostly shade | Some sun | Full sun |
|---|---|---|---|
| Below 68°FBelow 20°C | none | none | +2 oz0.05 L |
| 68 to 76°F20 to 24°C | −2 oz0.05 L | none | +3 oz0.10 L |
| 77°F and up25°C and up | −3 oz0.10 L | none | +7 oz0.20 L |
3. Body size
Bigger bodies make more heat on the same trail and sweat more. The rate scales with half your weight around 154 lb70 kg, between ×0.85 and ×1.3:
| Your weight | Factor |
|---|---|
| 130 lb or less59 kg or less | ×0.85 to ×0.92 |
| 154 lb70 kg | ×1.00 |
| 200 lb91 kg | ×1.15 |
| 255 lb and up116 kg and up | ×1.30 |
4. Hours on the trail, and the limits
Multiply the hourly rate by your hours on the trail. Three limits apply:
- At most 48 oz (1.5 quarts)1.4 liters an hour. The US Army guide caps hourly intake there: that is about as fast as the body takes water in, and drinking more raises the risk of hyponatremia.
- At most 12 quarts11.4 liters a day, the guide's daily limit. If a hike adds up to more, it is too long or too hot to do in one push.
- At least 17 oz0.5 liters, even for a short walk.
Worked example
A 160 lb73 kg hiker, 6 hours, 75°F,24°C, some sun, moderate effort: 20 oz0.60 L an hour from the table, no sun adjustment, ×1.02 for body size = 21 oz0.61 L an hour. Over 6 hours that is 124 oz,3.7 liters, about 8 lb3.7 kg of water, so the calculator also suggests planning a refill if the route has one.
Sources
- REI Expert Advice: How to Stay Hydrated on the Trail: about half a liter per hour of moderate activity in moderate temperatures.
- US Army Work/Rest and Water Consumption Table (TB MED 507): water per hour by heat category and workload, the sun and shade swing, and the hourly and daily limits.
- Grand Canyon National Park: Hike Smart: hikers can lose one to two liters of water an hour in summer heat, and drinking water without salt leads to hyponatremia.
Updated October 2026. Earlier versions of this calculator added a fixed amount for body weight and capped every result at 152 oz.4.5 liters. On long or hot hikes that gave too little water, sometimes half of what the guidance above asks for. If you used it for a long summer hike before, run your numbers again.
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Hydration Tips for Hikers
- Start hydrated: Drink a full bottle before your hike—don’t start on empty.
- Drink small amounts often: Sip regularly instead of chugging huge amounts at once.
- Watch your pee: Clear or pale yellow urine means you’re hydrated. Dark = drink more.
- Carry a backup: Always bring a bit more water than you think you’ll need, especially if you’re unsure about refill spots.
- Use electrolyte tabs: For long hikes, hot weather, or if you sweat a lot, use electrolyte tablets or drink mixes to replace lost salts.
- Know your route: Some trails have water sources (creeks, huts, taps). Bring a filter if you’ll refill from the wild.
- Eat your water: Fruits (like oranges, apples, cucumber) provide hydration and taste great on the trail.
- Adapt to altitude: You’ll need more water at higher elevations (above 2,500 meters/8,000 feet).
- Monitor for dehydration: Headache, dizziness, muscle cramps, or confusion are red flags. Stop and hydrate!
- Pack light, refill smart: If you know where clean water is available, you can carry less and refill as you go.
Hydration FAQ
Pay attention to thirst, energy, and urine color. If you feel thirsty, low on energy, or your pee is dark, drink more.
Yes, overhydration (hyponatremia) can be risky, especially if you’re not replacing lost salts. Don’t force water if you’re not sweating heavily or hiking long distances. Drinking to the calculator’s hourly rate, with salty snacks on long or hot hikes, keeps you on the safe side: it never goes above 1.5 quarts1.4 liters an hour.
For short hikes, water is enough. For longer hikes, or in hot weather, adding electrolytes (like sports drinks or electrolyte tablets) helps replace salt lost in sweat.
