Water Intake Calculator
Estimate your daily water needs from body weight, plus a little extra for exercise.
About 11.7 cups or 94.7 US fl oz per day, spread across your waking hours.
A common rule of thumb is about 35 ml of water per kilogram of body weight per day, plus roughly 350 ml for every 30 minutes of exercise. So a 70 kg person who trains 30 minutes needs 35 × 70 + 350 = 2,800 ml, which is 2.8 litres — about 11.7 cups or 94.7 US fluid ounces per day.
How the estimate works
There is no single official number for how much water a person should drink, so this tool uses a widely quoted heuristic rather than a clinical formula. It scales a baseline to your body size and adds a top-up for the fluid you lose through sweat during exercise. Bigger bodies and longer workouts push the number up.
The result counts total water, not only what you drink from a glass. Food, coffee, tea, milk, and juice all contribute, so your beverage target in practice is usually lower than the headline figure. Treat the number as a daily aim to spread across your waking hours, not a quota to hit in one sitting.
Baseline ≈ 35 ml per kg. Exercise adds ≈ 350 ml per 30 minutes. 1 cup = 240 ml; 1 L ≈ 33.814 US fl oz.
Worked example: 70 kg with 30 minutes of exercise
Scale the baseline to body weight, add the exercise top-up, then convert the millilitres to litres, cups, and fluid ounces:
- 1 Convert weight to kilograms. If you use pounds, multiply by 0.4536. A 154 lb person is about 70 kg.
- 2 Find the baseline. 35 ml × 70 kg = 2,450 ml from body weight alone.
- 3 Add for exercise. 350 ml × (30 ÷ 30) = 350 ml for a 30-minute session.
- 4 Total the millilitres. 2,450 + 350 = 2,800 ml, which is 2.8 litres per day.
- 5 Convert the units. 2,800 ÷ 240 ≈ 11.7 cups, and 2.8 × 33.814 ≈ 94.7 US fluid ounces.
Baseline water by body weight
Baseline only, at 35 ml per kg — before any exercise top-up. 1 cup = 240 ml; 1 L ≈ 33.814 US fl oz.
| Body weight | Litres/day | Cups | US fl oz |
|---|---|---|---|
| 50 kg (110 lb) | 1.75 L | ≈ 7.3 | ≈ 59.2 |
| 60 kg (132 lb) | 2.10 L | ≈ 8.8 | ≈ 71.0 |
| 70 kg (154 lb) | 2.45 L | ≈ 10.2 | ≈ 82.8 |
| 80 kg (176 lb) | 2.80 L | ≈ 11.7 | ≈ 94.7 |
| 90 kg (198 lb) | 3.15 L | ≈ 13.1 | ≈ 106.5 |
Reading the number sensibly
Hydration needs vary widely from person to person and day to day. Hot or humid climates, high altitude, a salty or high-protein diet, pregnancy, breastfeeding, illness with fever or vomiting, and certain medications all change how much fluid you need — sometimes substantially. A good real-world check is simple: pale-yellow urine and rarely feeling thirsty usually means you are drinking enough.
This is a rough informational estimate, not medical advice. If you have a heart, kidney, or other condition that affects fluid balance, or you are unsure how much to drink, ask a qualified healthcare professional.