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Water Intake Calculator by Body Weight
Calculate your daily water target straight from your body weight — the most reliable starting point. The bodyweight method uses about 33 mL of water per kilogram (the 30–35 mL/kg range), which is close to the familiar "half your weight in pounds, in ounces" rule. For a 70 kg (154 lb) person that base is about 2,310 mL, before any adjustment. This calculator then lets you add exercise (around 12 mL per minute to replace sweat) and a hot, humid climate (about +15%), so a 70 kg person training 45 minutes on a temperate day reaches roughly 2.85 L, or about 96 fl oz. Enter your weight in kilograms or pounds — pounds convert automatically — plus your exercise minutes and climate, and you get your target in mL, litres and fluid ounces, broken into base, activity and climate. This is beverage water; NASEM total-water figures (~3.7 L men / 2.7 L women) also count the ~20% you get from food. General hydration guidance, not medical advice.
Base = weight_kg × 33 (≈ half body-weight-lb in oz)
- 70 kg (154 lb) → 2,310 mL base before adjustments
- Add activity + climate for your personal target
Frequently asked questions
How do you calculate water intake by body weight?
Multiply your weight in kilograms by about 33 mL (the 30–35 mL/kg range) to get a base target. For a 70 kg person that is roughly 2,310 mL. In pounds, the shortcut is to drink about half your body weight in fluid ounces. Then adjust for exercise and hot weather to personalise the number.
Is the "half your body weight in ounces" rule accurate?
It is a reasonable shortcut for the bodyweight method — half your weight in pounds, drunk in fluid ounces, is close to 33 mL per kilogram. A 154 lb person would aim for about 77 oz as a base. It ignores activity and climate, though, which is why this calculator adds exercise and hot-weather adjustments on top.