Hydration Calculator
How the Hydration Calculator Works
The Hydration Calculator estimates how much water you’ll need on your trek or hike. It factors in your weight, the number of hours you’ll be hiking, temperature, sun exposure, and how hard you plan to go. Here’s exactly how each value is calculated—scroll down for simple tables.
1. Base Water Needs (Weight)
Your base hydration is calculated from your body weight:
- 0.4 oz per pound (13.2 ml per kilogram), then reduced by 20% for a safe, realistic baseline.
| Weight (kg) | Base Water (ml, after 20% reduction) | Weight (lbs) | Base Water (oz, after 20% reduction) |
|---|---|---|---|
| 50 | 528 | 110 | 35.2 |
| 60 | 634 | 132 | 42.2 |
| 70 | 739 | 154 | 49.3 |
| 80 | 844 | 176 | 56.3 |
| 90 | 950 | 198 | 63.3 |
2. Activity Level (per hour, after 15% reduction)
For every hour you trek, add the following based on your activity intensity:
| Activity Level | Add per Hour (oz) | Add per Hour (ml) |
|---|---|---|
| Easy | 0.85 | 25 |
| Moderate | 1.7 | 50 |
| Strenuous | 3.4 | 100 |
3. Sun Exposure (per hour, after 10% reduction)
More sun = more water needed. Add this amount for every hour, based on the sun level:
| Sun Exposure | Add per Hour (oz) | Add per Hour (ml) |
|---|---|---|
| Low | 1.8 | 53 |
| Medium | 2.7 | 80 |
| High | 3.6 | 106 |
4. Temperature Adjustment
Hotter temps mean higher water needs.
Multiply your subtotal (base + activity + sun) by the temperature factor:
| Ambient Temp (°C) | Hydration Increase (%) | Multiplier |
|---|---|---|
| Below 20°C | 0% | 1 |
| 20–24.9°C | 0.05 | 1.05 |
| 25–29.9°C | 0.1 | 1.1 |
| 30–34.9°C | 0.15 | 1.15 |
| 35–39.9°C | 0.2 | 1.2 |
| 40°C or higher | 0.25 | 1.25 |
5. Final Safety Buffer
After all other calculations, add a final 10% to cover for any unexpected sweat loss or extreme conditions. The calculator also caps your total intake at 4.5 liters for safety.
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. For most hikes, sticking to the calculator’s cap (4.5L) is safe.
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.
