Water Intake Calculator — How Much Water Should I Drink?
Find your personalised daily water intake goal in litres, cups, and fluid ounces based on your body weight, activity level, and climate.
💧 Calculate Your Daily Water Intake
How Daily Water Needs Are Calculated
This calculator uses the weight-based method recommended by most nutrition organisations: 35–50 ml of water per kilogram of body weight per day, adjusted upward for activity level and heat. The base rate of 35 ml/kg applies to sedentary adults in temperate climates; active individuals in hot environments can need 50+ ml/kg.
The European Food Safety Authority (EFSA) recommends 2.0 litres/day for women and 2.5 litres/day for men as adequate daily intake from all sources including food. The US National Academies recommend 2.7 litres/day for women and 3.7 litres/day for men from all sources. Approximately 20% of daily water needs typically come from food — so the drinking target is 80% of total needs. This calculator accounts for biological sex: women's results are adjusted down by approximately 15% to align with lower average recommendations, while keeping weight and activity as the primary drivers.
Factors That Increase Water Needs
Exercise and physical activity
Sweat losses during exercise range from 0.5 litres/hour for light activity in cool conditions to over 2 litres/hour for intense exercise in the heat. The American College of Sports Medicine recommends drinking 500 ml (17 oz) in the 2 hours before exercise, and 150–250 ml every 15–20 minutes during exercise. After exercise, aim to replace 125–150% of fluid lost (weigh yourself before and after — each kg lost = approximately 1 litre of fluid deficit).
Heat and humidity
High temperatures increase sweat rate and respiratory water loss. Humidity reduces evaporative cooling, increasing the sweat volume needed to maintain body temperature. Working or exercising in temperatures above 35°C / 95°F can increase daily water needs by 1–2 litres compared to temperate conditions.
Pregnancy and breastfeeding
Pregnant women need approximately 300 ml more per day than baseline. Breastfeeding women need an additional 700–1,000 ml/day to account for milk production — roughly one extra litre compared to pre-pregnancy needs.
Illness
Fever, vomiting, and diarrhoea all significantly increase fluid and electrolyte losses. For each degree Celsius of fever above 37°C, fluid needs increase by approximately 10–15%. During gastrointestinal illness, oral rehydration solutions (containing both water and electrolytes) are more effective than plain water for replacing losses.
Water Intake Reference by Weight
| Body Weight | Sedentary | Lightly Active | Very Active |
|---|---|---|---|
| 50 kg / 110 lbs | 1.75 L | 2.0 L | 2.5 L |
| 60 kg / 132 lbs | 2.1 L | 2.4 L | 3.0 L |
| 70 kg / 154 lbs | 2.45 L | 2.8 L | 3.5 L |
| 80 kg / 176 lbs | 2.8 L | 3.2 L | 4.0 L |
| 90 kg / 198 lbs | 3.15 L | 3.6 L | 4.5 L |
| 100 kg / 220 lbs | 3.5 L | 4.0 L | 5.0 L |
Signs of Dehydration and How to Stay Hydrated
The simplest hydration indicator is urine colour. Pale straw yellow means well hydrated. Dark yellow or amber means you need more water. Clear urine may indicate overhydration. Check first thing in the morning — dark morning urine is normal after sleep; it should lighten with morning fluid intake.
Practical strategies for hitting your daily target:
- Start each morning with a large glass of water (500 ml) before coffee or food
- Keep a refillable bottle on your desk — if you can see it, you'll drink from it
- Drink a glass of water before each meal — it also supports satiety
- Set a hourly reminder on your phone if you consistently forget to drink
- Eat water-rich foods: cucumber (96% water), watermelon (92%), strawberries (91%), lettuce (95%)
- Replace soft drinks with sparkling water — same ritual, far healthier
Hydration During Exercise
Exercise hydration requires more active management than everyday drinking. Pre-exercise: drink 400–600 ml in the 2 hours before a workout. During exercise: drink 150–250 ml every 15–20 minutes for sessions lasting under an hour. For sessions over 60–90 minutes, consider an electrolyte drink rather than plain water — sweat contains sodium, potassium, and magnesium that plain water does not replace.
The simplest post-exercise rehydration strategy: weigh yourself before and after exercise. For each kilogram of body weight lost, drink 1.2–1.5 litres of fluid over the next few hours. Don't try to drink it all at once — distribute it over 2–4 hours to allow absorption. A sports drink, diluted juice, or water with a pinch of salt and a banana provides both fluids and electrolytes.
Water Quality and Types of Hydration
All non-alcoholic beverages contribute to hydration. Water (still or sparkling) is ideal. Milk is actually one of the most hydrating beverages studied, outperforming sports drinks for rehydration after exercise due to its protein and electrolyte content. Fruit juice contributes to hydration but adds significant sugar calories. Herbal teas are excellent. Caffeinated teas and coffees at moderate intake are net positive. Alcohol is a net dehydrator and should not be counted toward daily intake.