Find your daily hydration target based on body weight, exercise, and climate.
Hydration is one piece of the puzzle — see your complete calorie and macro targets too.
Calculate My Macros 🚀This calculator uses the widely cited baseline of roughly 2/3 ounce of water per pound of body weight (about 30-35 mL per kg), then adds extra fluid for exercise — a commonly used rule of thumb of an additional 12 oz (350 mL) for every 30 minutes of exercise — and adjusts upward for hot or humid conditions, since sweat losses increase substantially in heat.
The popular "8 glasses a day" guideline is a rough, one-size-fits-all rule of thumb that doesn't account for body size, activity, or climate at all. A 130 lb person and a 220 lb person have meaningfully different baseline fluid needs simply due to body mass — scaling intake to body weight gives a far more individualized, useful target than a flat number everyone is told to follow regardless of size.
Thirst is a late indicator — by the time you feel thirsty, you're often already mildly dehydrated. Better day-to-day indicators include urine color (pale yellow is well-hydrated; dark yellow suggests you need more fluids) and energy levels, since even mild dehydration is linked to fatigue and reduced concentration.
Yes — drinking far more water than your body needs in a short period can lead to a dangerous condition called hyponatremia, where sodium levels in your blood become diluted. This is rare from normal daily drinking habits but has happened in extreme cases like water-drinking contests or excessive intake during endurance events without adequate electrolyte replacement.
Despite the old myth, moderate caffeine intake doesn't cause a meaningful net fluid loss for regular coffee drinkers — the mild diuretic effect is largely offset by the fluid in the beverage itself. Coffee and tea count toward your total daily fluid intake.
Generally less than training days, since you're not losing extra fluid through sweat. Lower the "Exercise Today" field to 0 on rest days to get an accurate baseline target for that day specifically.
A common guideline is to drink 0.5 to 0.67 ounces of water per pound of body weight per day (roughly 30–40 ml per kg). So a 150 lb person needs 75–100 oz (about 9–12 cups) as a baseline, before adding for exercise or heat. This calculator applies that formula automatically — just enter your weight.
Dogs generally need about 1 ounce (30 ml) of water per pound of body weight per day. A 50 lb dog needs roughly 50 oz (about 6 cups) daily under normal conditions — more if it's hot, they're active, or they eat mostly dry kibble. This human water intake calculator isn't designed for pets, but you can apply the 1 oz/lb rule directly to estimate your dog's water needs.