Water Intake Calculator
How much water to drink per day by weight and activity.
Input sheet
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Staying hydrated supports energy, focus, digestion, and exercise performance, yet most people drink by habit rather than need. This tool sets a daily baseline from your body weight and adds for the sweat you lose during exercise.
How it works
About half your body weight in ounces, plus ~12 oz per 30 minutes of exercise. Hot climates need more.
The estimate starts at about half your body weight in ounces, then adds roughly 12 ounces for every 30 minutes of exercise to replace what you sweat out. It's a practical baseline, not a medical prescription.
Your real needs shift with climate, altitude, illness, pregnancy, and caffeine or alcohol intake. Food and other drinks also contribute water, so this figure is a target for deliberate hydration, not the only fluid you'll take in.
Ounces per day = weight(lb) × 0.5 + (exercise minutes ÷ 30) × 12.
Worked examples
A 175 lb person who exercises 30 minutes a day. → About 100 oz/day (roughly 2.9 L or 12.4 cups).
175 × 0.5 + (30 ÷ 30) × 12 = 87.5 + 12 = 99.5 oz.
A 140 lb person who doesn't exercise that day. → About 70 oz/day (roughly 2.1 L).
140 × 0.5 + 0 = 70 oz.
Tips & gotchas
- Spread intake across the day rather than chugging — your body absorbs steady sips far better than a large dose at once.
- Use urine color as a quick check: pale yellow means well hydrated, dark means drink more.
- Add extra in hot or humid weather, at altitude, and when sick — this baseline assumes moderate conditions.
- Don't drastically overdrink; consistently flushing far past thirst can dilute electrolytes and isn't necessary.
FAQ
Does coffee or tea count toward my total?
Mostly yes. The mild diuretic effect of normal caffeine intake is small, so the fluid in coffee and tea still counts. Water and unsweetened drinks are simply the cleanest sources.
Is the old '8 glasses a day' rule right?
It's a rough average, not a personalized number. Scaling to your body weight and activity, as this tool does, fits your actual needs better than a fixed eight cups.
Can I drink too much water?
Rarely, but yes — drinking far beyond thirst over a short window can dilute blood sodium. Use the estimate as a target and let thirst guide the fine-tuning.
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