Daily water calculator
This calculator needs JavaScript. The quick-reference table below works without it, and the formula is just above it.
How it works
The base blends two things: 33 ml per kilogram of body weight (kept between 1.5 and 4 litres), and the European Food Safety Authority's adequate intake, of which about 80% comes from drinks. Blending keeps very light and very heavy people in a sensible range. A workout adds what you sweat, about 0.7 litres an hour at moderate effort scaled by your size, of which you replace about 80%. A hot day adds half a litre. Coffee and tea count: moderate caffeine doesn't dehydrate you.
base = ½ × (33 ml × kg, kept to 1.5–4 L) + ½ × 1.8 L
workout = 0.7 L/h × (kg ÷ 70, kept to 0.7–1.4) × hours × 0.8 (up to 2.5 L)
hot day = + 0.5 L
total = base + workout + hot day, rounded to 50 ml
Quick reference
| Weight | Rest day | 60-minute workout | Workout, hot day |
|---|---|---|---|
| 50 kg (110 lb) | 1.7 L | 2.1 L | 2.6 L |
| 60 kg (132 lb) | 1.9 L | 2.4 L | 2.9 L |
| 70 kg (154 lb) | 2.05 L | 2.6 L | 3.1 L |
| 80 kg (176 lb) | 2.2 L | 2.85 L | 3.35 L |
| 90 kg (198 lb) | 2.4 L | 3.1 L | 3.6 L |
| 100 kg (220 lb) | 2.55 L | 3.35 L | 3.85 L |
| 110 kg (243 lb) | 2.7 L | 3.5 L | 4 L |
How Auralo does this
Auralo sets this target every day from your latest weight in Apple Health, today's workouts and how hard they were, and, if you turn on weather-aware advice, today's heat (+250, +500 or +750 ml as it gets hotter). It spreads what's left across your day, adds a glass before and after a workout, and Drip, your water buddy, shows where you are on the Lock Screen.
Questions
Does coffee count toward water?
Yes. Moderate caffeine isn't meaningfully dehydrating, so coffee and tea count.
Is 8 glasses a day right?
It's a rough average. Your need depends on your size, your activity and the weather, which is what this calculator accounts for.
Can I drink too much?
Yes, though it's rare. Drinking far more than you sweat during long events can be dangerous. On long sessions, weigh yourself before and after and replace about what you lost.
Is this medical advice?
No. It's wellness information. If you have kidney, heart or other conditions that affect fluid balance, follow your clinician's guidance.
Sources
- EFSA Panel on Dietetic Products, Nutrition, and Allergies. Scientific opinion on dietary reference values for water. EFSA Journal 2010;8(3):1459.
- American College of Sports Medicine; Sawka MN et al. Exercise and fluid replacement. Med Sci Sports Exerc 2007;39(2):377–390.
Wellness information, not medical advice. If you have a health condition, follow your clinician's guidance.