Worked examples (so you trust the number)

These examples show exactly what happens behind the scenes. Your results may differ because your climate/activity inputs differ.

• Example A (common case): 165 lb person, 45 min activity, warm climate, 2 coffees, 0 alcohol.
  Convert: 165 lb ÷ 2.20462 = 74.8 kg. Base = 35 × 74.8 = 2618 ml. Activity = 700 × (45/60) = 525 ml. Climate (warm) = 250 ml. Caffeine buffer = 2 × 100 = 200 ml.
  Total ≈ 2618 + 525 + 250 + 200 = 3593 ml/day = 3.59 L ≈ 121.5 oz ≈ 15.2 cups.
• Example B (hot + active): 70 kg person, 90 min activity, hot climate, 0 caffeine, 1 alcohol.
  Base = 35 × 70 = 2450 ml. Activity = 700 × (90/60) = 1050 ml. Climate (hot) = 500 ml. Alcohol buffer = 1 × 350 = 350 ml.
  Total ≈ 2450 + 1050 + 500 + 350 = 4350 ml/day = 4.35 L ≈ 147.1 oz.
• Example C (low activity, indoor): 130 lb person, 0 min activity, normal climate.
  130 lb = 59.0 kg. Base = 35 × 59.0 = 2065 ml/day = 2.07 L.

How to actually use your result (the practical part)

A number is only useful if it turns into behavior. Here’s a simple “hydration system” using your output:

• Pick your container: 500 ml bottle or 16.9 oz bottle (common store size).
• Use bottle targets: If your result says “7 bottles,” that’s your daily scoreboard.
• Front-load lightly: 25–35% by noon helps most people avoid “night chugging.”
• Anchor to routines: 6–10 sips after bathroom breaks is “automatic hydration.”
• Match sweaty moments: if your workout is intense, distribute extra water around it.
• Don’t overdo it: extremely high water intake in a short window can be unsafe.

If you have kidney disease, heart failure, hyponatremia risk, or you’ve been told to limit fluids, follow your clinician’s guidance instead of calculator targets.

FAQs

• Is “35 ml per kg” a perfect rule? No single rule fits everyone. It’s a solid planning baseline used in many practical hydration guides, then adjusted for sweat, heat, and your day. This calculator adds those adjustments so the result is more realistic.
• Does coffee dehydrate you? Normal caffeine intake is often not strongly dehydrating for regular caffeine users, but people still report “dryness” and extra bathroom trips. This calculator uses a small buffer (+100 ml/cup) as a practical hedge, not as a claim that coffee “cancels out” water.
• What about electrolytes? If you sweat heavily (long workouts, hot climate), electrolytes can matter. This tool estimates water volume only. For long-duration intense exercise, consider electrolytes per standard sports guidance.
• How accurate is the “exercise add-on”? Sweat rate varies a lot. We use ~700 ml per hour as a middle-of-the-road estimate for many adults doing moderate activity. If your workouts are very light, your true add-on may be lower; if you sweat heavily, it may be higher.
• Should I drink the exact number every day? Use the result as a target range. If you’re not thirsty, don’t force huge volumes. Pay attention to thirst, urine color, and how you feel—especially in heat or long workouts.
• Can drinking too much water be dangerous? Yes. Very high intake in a short time can dilute sodium (hyponatremia). Spread your intake across the day and avoid extreme chugging. If you’re unsure, seek medical guidance.
• Does “water intake” include tea, soups, or fruit? In real life, yes—many foods and drinks contribute to hydration. This calculator outputs a simple “water target” so it’s easy to track. If you eat watery foods/soups often, you may naturally hit the target with less plain water.
• How do I make this viral/shareable? Post your result as “bottles/day” and challenge friends. Example: “I’m a 6-bottle/day human—beat me for 7 days.” Screenshots work great with the meter + bottle target.