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Understanding Your Hydration Needs
Base formula: ~35ml per kg of body weight (or 0.5-1 oz per lb). This covers basic metabolic needs for a temperate climate with minimal activity.
Activity Level Multipliers
- Sedentary: No adjustment — basic metabolic needs only
- Light: +10% — compensates for occasional movement
- Moderate: +20% — regular exercise creates more sweat loss
- Active: +30% — daily training requires consistent hydration
- Very Active: +40% — intense training demands maximum water intake
Exercise Adjustment
Add approximately 500-1000ml per hour of exercise. The calculator uses 700ml/hour as a balanced estimate. If you're exercising intensely or in heat, aim for the higher end.
Signs of Dehydration
- Thirst
- Dry mouth
- Darker urine
- Headache
- Fatigue
- Reduced focus
- Dizziness
- Rapid heartbeat
- Confusion
Frequently Asked Questions
Does coffee count toward my water intake?
Yes! While caffeine has mild diuretic effects, the water in coffee and tea still contributes to hydration. However, water remains the best choice for pure hydration.
Can I drink too much water?
Yes, though it's rare. Overhydration (hyponatremia) can dilute blood sodium levels. Spread your intake throughout the day and don't force excessive amounts.
Should I drink more water when sick?
Generally yes, especially with fever, vomiting, or diarrhea. These conditions increase fluid loss. Consult a doctor for specific guidance.
How does food contribute to hydration?
About 20% of daily water intake comes from food. Fruits and vegetables like watermelon, cucumber, and oranges are particularly hydrating.
Privacy & Limitations
- All calculations run entirely in your browser -- nothing is sent to any server.
- Results are estimates and should not replace professional medical advice.
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Hydration Calculator FAQ
What is Hydration Calculator?
Hydration Calculator is a free health tool that helps you Calculate daily water intake needs.
How do I use Hydration Calculator?
Enter your input values, review the calculated output, and adjust inputs until you reach the result you need. The result updates in your browser.
Is Hydration Calculator private?
Yes. Calculations run locally in your browser. Inputs are not uploaded to a server by default, and refreshing the page clears session data.
Does Hydration Calculator require an account or installation?
No. You can use this tool directly in your browser without sign-up or software installation.
How accurate are results from Hydration Calculator?
This tool applies standard formulas or deterministic processing logic for estimates. For medical, legal, tax, or investment decisions, verify with a qualified professional.
Can I save or share outputs from Hydration Calculator?
You can bookmark this page and copy outputs manually. Results are not persisted in your account and are typically not embedded in the URL.