WATER INTAKE
CALCULATOR
Find your personalised daily water target based on weight, activity level, and climate.
This calculator provides a general estimate for informational purposes only and is not a substitute for professional medical advice. If you have a health condition affecting fluid balance, talk to a doctor or registered dietitian before changing your fluid intake.
| Guideline | Target | Notes |
|---|---|---|
| Sedentary adult (per kg) | 30–35 ml/kg | ~2.1–2.5L for 70kg person |
| Active adult (per kg) | 35–45 ml/kg | Add 500ml per 30min exercise |
| Hot climate adjustment | +10–20% | Increase for heat/humidity |
| NAS: Adult men | 3.7L total | From all food + drink sources |
| NAS: Adult women | 2.7L total | From all food + drink sources |
What This Calculator Does
The Water Intake Calculator gives your personalised daily hydration target based on body weight, activity level, and climate. It uses the National Academies of Sciences 30–35ml per kg guideline plus an exercise adjustment.
The Formula Explained
Base: 30–35ml per kg body weight. Add 500ml per 30 minutes of exercise. Hot climate: add 10–20%. Example: 75kg, moderately active → 75 × 33ml = 2,475ml base + 500ml exercise = ~3L daily target.
What Your Result Means
Even mild dehydration (a loss of roughly 1–2% of body weight in fluid) has been associated with reduced concentration and increased perceived effort during exercise in some studies, though individual responses vary. The "8 glasses a day" rule is not based on strong scientific evidence — individual needs can vary by 2–3× depending on body size, activity level, and climate. Urine colour is a commonly used real-time indicator: pale yellow generally suggests adequate hydration.
Calorie Calculator for complete nutrition planning · Read: How Much Water Should You Drink?
Who Should Be Extra Mindful of Hydration
Hydration needs are not identical for everyone. Older adults may have a blunted thirst response and can benefit from tracking intake rather than relying on thirst alone. People who are pregnant or breastfeeding, those exercising in hot weather, and anyone managing a fever, vomiting, or diarrhoea typically need more fluid than the baseline estimate above. If you have a heart, kidney, or liver condition that affects fluid balance, follow your healthcare provider's specific guidance rather than a general calculator, since your safe intake range may be different from the general population.