Free tool
Water intake calculator
“Eight glasses a day” is a number with no evidence behind it. How much water you should drink a day scales with your bodyweight, how much you sweat and how hot it is where you live. Enter those three and this calculates your daily water intake in litres, millilitres and glasses.
Updated
Where the numbers come from
The baseline is about 35 ml per kilogram of bodyweight, which is the figure most clinical guidance converges on for healthy adults.
Exercise adds roughly 500 ml per hour of training. Hot or humid conditions add another 500 ml or so across the day, warm conditions about half that.
Food contributes 20–30% of most people’s fluid intake, and tea, coffee and milk all count toward the total. The idea that caffeine dehydrates you does not survive contact with the evidence at normal intakes.
Quick reference
Daily water intake by body weight.
Baseline figures at about 35 ml per kilogram, for a mild climate and no exercise. Add around 500 ml for every hour of training and up to 500 ml on a hot day. Food supplies another 20–30% on top of this.
| Body weight | Litres per day | Glasses (250 ml) | US fl oz |
|---|---|---|---|
| 50 kg (110 lb) | 1.75 L | 7 | 59 oz |
| 60 kg (132 lb) | 2.1 L | 8–9 | 71 oz |
| 70 kg (154 lb) | 2.45 L | 10 | 83 oz |
| 80 kg (176 lb) | 2.8 L | 11 | 95 oz |
| 90 kg (198 lb) | 3.15 L | 12–13 | 106 oz |
| 100 kg (220 lb) | 3.5 L | 14 | 118 oz |
How much water should you drink to lose weight?
The same amount as the calculator gives you. There is no separate “weight loss” water target, and drinking extra beyond thirst does not burn meaningful calories. The often-quoted effect of cold water on metabolism is a few calories a glass.
Where water genuinely helps is indirectly. A large glass 20–30 minutes before a meal modestly reduces how much people eat in studies, particularly older adults. Swapping sweetened drinks for water is the bigger lever: a day of sugary chai, juice and a soft drink can add 300–500 calories that rarely get logged.
One caution for anyone watching the scale: a salty meal or a high-carb day makes you hold a litre or more of water, which shows up as a kilogram the next morning. That is not fat, and drinking less will not fix it. Water and weight loss, in more detail →
Simpler than a target
Just check the colour.
Pale straw means you are fine. Dark yellow means drink more. Completely clear means you are probably drinking more than you need, which is harmless but unnecessary.
Thirst is a reliable signal for most healthy adults under normal conditions. The main exceptions are older adults, whose thirst response blunts with age, and anyone training hard in heat.
One practical note for anyone tracking calories: sweetened drinks are where a startling number of unlogged calories hide. A day of sweetened chai, juice and a soft drink can quietly reach 500 calories.
Frequently asked questions
How much water should I drink a day?
Most adults need roughly 30–40 ml per kilogram of body weight from drinks, which is 2–3 litres for most people. Men generally need more than women because they are larger on average. Exercise and hot weather push the number up, and food provides a further 20–30% of total fluid.
Is 3 litres of water a day too much?
Not for most healthy adults, especially larger people or anyone active in a warm climate. It is only a problem if it forces you to drink well past thirst, or if you have a heart or kidney condition where fluid is restricted.
Do tea and coffee count?
Yes. At normal intakes the mild diuretic effect of caffeine does not offset the fluid in the drink. Milk, juice and soft drinks all count too, though the latter two bring calories with them.
Does drinking water help with weight loss?
Indirectly. A glass before a meal modestly reduces how much people eat, and thirst is sometimes misread as hunger. Water itself does not burn fat.
Can you drink too much water?
Yes, though it is rare. Drinking several litres in a short period can dilute blood sodium dangerously. Spread intake across the day rather than in large bursts.
Does BetterCal track water?
No, deliberately. Water logging is one of the small frictions that makes tracking feel like a chore, and it does not affect your calorie or macro numbers. BetterCal focuses on food.
Next step
Food is the part worth tracking.
Free to start on iPhone and Android.
