Water intake calculator

How much water you actually need in a day, worked out from your bodyweight and your training rather than a number someone made up in the 1940s.

Milo

Weight (kg)

Exercise (min/day)

Hot or humid climate?

Your target will appear here.

How this is worked out

The baseline is about 35ml per kilogram of bodyweight, which scales with you: a 55kg person and a 110kg person do not have the same requirement, and any fixed number of glasses gets one of them wrong.

daily ml ≈ weight(kg) × 35, plus ~500ml per 30 min of training

Training adds roughly half a litre per half hour, more in heat, and a hot or humid climate adds around 15% on top of the baseline. Sweat rates vary enormously between people, so treat these as starting points.

About the eight-glasses rule: it has no research behind it. The usual origin story is a 1945 US recommendation of 2.5 litres a day, which also said, in the sentence everyone forgets, that most of that comes from food.

Tea and coffee count. The idea that caffeine dehydrates you doesn’t survive contact with the evidence at normal intakes: the fluid more than covers the modest diuretic effect.

The number is the easy part

Any calculator can hand you a figure. The hard bit is the next three months: eating roughly to it, noticing when it stops working, and changing it. Milo is a coach you text like a friend. You log what you ate in a sentence, and it learns your patterns, notices when your weight stalls, and adjusts the target from what you actually did rather than from a formula.

See how Milo works

Common questions

How do I know if I'm drinking enough?

Pale straw-coloured urine, and not feeling thirsty. Both are better daily guides than hitting a target exactly. Dark urine, headaches or fatigue in the afternoon are the usual signs of falling short.

Can I drink too much water?

Yes, though it’s rare. Drinking far more than you lose can dilute blood sodium, which is dangerous. It mostly affects endurance athletes drinking heavily during long events. Spreading intake across the day rather than forcing litres at once avoids it entirely.

Do tea and coffee count?

Yes. At normal intakes the diuretic effect of caffeine is small and easily outweighed by the fluid in the drink. Alcohol is the genuine exception: it increases fluid loss meaningfully.

Does drinking water help with weight loss?

Indirectly. A glass before a meal modestly reduces how much people eat in trials, and thirst is sometimes mistaken for hunger. It’s a small effect, not a mechanism, and no amount of water substitutes for a calorie deficit.

Other calculators

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Sleep debt calculator — How far behind a week of short nights has put you.
TDEE calculator — How many calories you burn in a day, and what to eat for your goal.
Calorie deficit calculator — How long a given deficit takes to reach your goal weight.
Protein calculator — Your daily protein target, based on lean mass rather than bodyweight.

These are estimates from population averages, not measurements of you. Individual metabolism varies by roughly ±10% around any formula. Nothing here is medical advice — if you have a health condition, are pregnant, or are under 18, talk to a healthcare professional before changing how you eat or train.