How much water you need depends on your body size, how active you are and how hot it is. This calculator gives a personal daily water goal in litres, ounces and glasses.
How the estimate works
- Base need: about 35 ml per kg of body weight (≈ 0.5 oz per lb).
- Exercise: about 350 ml (12 oz) extra for every 30 minutes of activity.
- Hot or humid weather: about 500 ml extra.
Example: a 70 kg person who exercises 30 minutes a day needs roughly 2.8 litres (≈ 95 oz) of fluid a day.
What official guidance says
Health authorities give total fluid intake (from drinks and food) of roughly 2.7 litres a day for women and 3.7 litres for men. About 20% typically comes from food such as fruit, vegetables and soups, so drinks make up the rest.
Signs you’re well hydrated
- Pale yellow urine.
- Rarely feeling thirsty.
- No headaches or fatigue from dehydration.
Easy ways to drink more
- Carry a refillable bottle and finish it by set times.
- Drink a glass with every meal.
- Eat water-rich foods like cucumber, watermelon and oranges.
- Tea and coffee count towards your fluid intake too.
Can you drink too much?
Yes. Drinking very large amounts quickly can lower blood sodium (hyponatremia). Spread intake through the day. People with kidney, heart or liver conditions should follow their doctor’s fluid advice.
This calculator is for general information and is not medical advice.
Daily water goal by body weight (30 minutes of exercise, mild climate)
| Weight | Litres per day | US fl oz | 250 ml glasses |
|---|---|---|---|
| 50 kg (110 lb) | 2.1 | 71 | 8 |
| 60 kg (132 lb) | 2.5 | 83 | 10 |
| 70 kg (154 lb) | 2.8 | 95 | 11 |
| 80 kg (176 lb) | 3.2 | 107 | 13 |
| 90 kg (198 lb) | 3.5 | 118 | 14 |
| 100 kg (220 lb) | 3.9 | 130 | 15 |
These figures cover total fluids from drinks. If you eat lots of fruit, vegetables and soups, you may need a little less from drinks.
Hydration for exercise
- Before: drink about 400–600 ml in the 2 hours before a workout.
- During: sip regularly; for sessions longer than an hour or in heat, a sports drink with electrolytes helps replace sodium.
- After: weigh yourself before and after a long session – each kilogram lost is roughly 1–1.5 litres to replace.
Who needs more (or less)?
- More: hot climates, high altitude, physical jobs, fever or vomiting, and pregnancy or breastfeeding (talk to your doctor for specific advice).
- Less or monitored: people with heart failure, kidney disease or certain medications may be told to limit fluids.
- Older adults often feel less thirsty, so drinking on a schedule can help.
Water from food
Many foods are mostly water: cucumber and lettuce (~95%), watermelon and strawberries (~91%), oranges (~87%), yoghurt (~85%) and cooked rice (~70%). That’s one reason your drinks target can be lower than total fluid recommendations.
Real-life scenarios
- Office worker: Neha weighs 58 kg and walks 30 minutes a day. Her goal is about 2.4 litres – roughly a 1-litre bottle in the morning, another in the afternoon, plus drinks with meals.
- Gym-goer: Jake weighs 85 kg and trains for an hour. His estimate is about 3.7 litres, with extra water around workouts.
- Hot summer: In 40°C weather, add at least half a litre and drink before you feel very thirsty.
- Older adult: Thirst signals weaken with age, so a simple routine – a glass with each meal and one mid-morning and mid-afternoon – helps meet needs.
Building a hydration habit
Most people don’t need to count every sip. Set a few anchors: a glass of water when you wake up, one with each meal, and a bottle on your desk you refill twice. Check your urine colour – pale yellow is a good sign. Use the calculator to set a target, then let habits do the work.
Related calculators
- Running pace calculator – plan training runs
- Sleep calculator – better bedtimes
- Cups to grams – kitchen conversions including ml
FAQs
Does coffee dehydrate you?
Not in normal amounts. The fluid in coffee and tea outweighs their mild diuretic effect, so they count toward your daily intake.
Is 4 litres of water a day too much?
For a large, active person in hot weather it can be reasonable. For a small, sedentary person it’s more than needed. Spread intake through the day and follow thirst.