How to work out your water goal by hand
- Start from your weight. Multiply your weight in kg by 33 ml (or your weight in pounds by 0.5 fl oz). For 70 kg, that's 2,310 ml, about 2.3 liters.
- Add your exercise. Add about 0.6 liters (20 fl oz) for each hour of exercise, or 0.8 liters (27 fl oz) in hot or humid weather.
- Add pregnancy or breastfeeding. Add 0.3 liters (10 fl oz) a day if you're pregnant, or 0.7 liters (24 fl oz) if you're breastfeeding.
- Spread it over the day. Round to the nearest 50 ml and drink it across the day, with meals and around exercise, rather than all at once.
How the water calculator works
The calculator builds a daily drinks goal in four steps:
- A starting point from your weight. 33 ml for every kg of body weight, rounded to the nearest 50 ml. That’s the default water goal in the Calorix app, so the number here matches the one the app sets for you.
- Exercise. About 0.6 liters for each hour of exercise on a typical day, or 0.8 liters in hot or humid weather. The American College of Sports Medicine’s position stand on fluid replacement describes 0.4 to 0.8 liters an hour as a reasonable range during exercise, with the higher end for heavier people and warmer conditions.
- Pregnancy or breastfeeding. 300 ml a day extra in pregnancy and 700 ml while breastfeeding, the additions in the EFSA reference values for water.
- Rounding. The total is rounded to the nearest 50 ml, and shown in glasses of 250 ml or cups of 8 fl oz.
Then it compares your goal with two official references, so you can see whether it’s in the usual range.
The reference intakes
Both are adequate intakes for healthy adults: amounts that appear to keep people well hydrated, not strict requirements. They count total water, from drinks and food:
| Group | EFSA (Europe), total | From drinks (about 80%) | National Academies (US), total | From beverages |
|---|---|---|---|---|
| Women | 2.0 L | about 1.6 L | 2.7 L | about 2.2 L |
| Men | 2.5 L | about 2.0 L | 3.7 L | about 3.0 L |
| Pregnancy | 2.3 L | about 1.8 L | 3.0 L | about 2.3 L |
| Breastfeeding | 2.7 L | about 2.2 L | 3.8 L | about 3.1 L |
Why do they differ? The National Academies based their figures on the median water intake of healthy Americans in a national survey, while EFSA combined observed intakes in Europe with the amounts that keep urine at a healthy concentration. EFSA notes that its values apply to moderate temperatures and moderate activity; needs rise with heat and exercise.
Worked examples
| Person | Starting point (33 ml/kg) | Extra | Daily drinks goal |
|---|---|---|---|
| 60 kg (132 lb), desk job, mild weather | 2.0 L | none | 2.0 L (68 fl oz) |
| 80 kg (176 lb), runs 1 hour, mild weather | 2.65 L | +0.6 L | 3.25 L (110 fl oz) |
| 70 kg (154 lb), 1 hour of exercise in the heat | 2.3 L | +0.8 L | 3.1 L (105 fl oz) |
| 65 kg (143 lb), breastfeeding | 2.15 L | +0.7 L | 2.85 L (96 fl oz) |
What counts toward your water
- All drinks count: water, sparkling water, tea, coffee, milk and juice. The National Academies found that caffeinated drinks contribute to hydration much like other drinks.
- So does food. Fruit, vegetables, soups and yogurt are mostly water, and food supplies about a fifth of the total. That’s why the drinks goal is lower than the reference intakes.
- Alcohol isn’t a good way to hydrate, so it’s best not counted.
Signs you may need more
- Thirst, dark yellow urine, a dry mouth, headaches or feeling unusually tired.
- Exercising in the heat. Weighing yourself before and after a workout shows your sweat loss: the ACSM suggests drinking about 1.5 liters for each kilogram lost when you need to recover quickly.
- Illness with fever, vomiting or diarrhea.
When to be careful
Some people need a different target, so follow your doctor’s advice if:
- You have kidney, heart or liver disease, or you’ve been asked to limit fluids.
- You take medication that affects fluid balance, such as diuretics.
- You’re an older adult: thirst becomes a less reliable signal with age, so regular drinks across the day help.
More isn’t always better. During long endurance events, drinking far more than you sweat out can lower the sodium in your blood to dangerous levels (hyponatremia), which is why the ACSM recommends drinking to replace losses, not to excess.
Tracking water in Calorix
Water tracking is part of Calorix 2.0. Add a glass in one tap from the app or a widget, and Toasty cheers every glass. Your goal starts from the same 33 ml per kg as this calculator and you can set your own. For your full daily targets, the macro calculator shows water next to calories, protein, carbs and fat.
