The eight glasses rule came from nowhere in particular and it ignores two things that decide fluid needs: how much you weigh and how much you sweat. In Malaysia the second one is not optional.
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How the estimate is built
- Baseline: about 33 ml per kilogram of body weight
- Exercise: about 12 ml per minute, which is roughly 350 to 700 ml an hour
- Heat: 300 ml for some time outdoors, 700 ml for most of the day outdoors or in a hot workplace
The total counts all fluid, not plain water alone. Soup, unsweetened drinks and water-heavy food all count. Coffee and tea count too, since the mild diuretic effect does not cancel the fluid they carry.
Urine colour beats counting
Pale straw through the day means you are about right. Dark yellow means behind. Completely clear all day usually means more than needed, which is not harmful for most people but is worth noticing if you are forcing litres to hit a target. The number here is a starting estimate; what your urine does is the feedback.
Sweat loss is salt loss too
An hour of hard work in Malaysian heat can cost well over a litre of sweat, and sweat carries sodium. Replacing a large loss with plain water alone leaves you diluted rather than hydrated, which shows up as headache, cramping and continued thirst despite drinking. Past roughly two hours of heavy sweating, fluid with some salt in it does more than plain water.
When this calculator does not apply to you
If you have kidney disease, heart failure or liver disease, your doctor may have set a fluid restriction. That figure overrides anything calculated here, because in those conditions the body cannot clear a surplus and the surplus itself is the risk. The same applies to certain diuretic and lithium prescriptions. If you are on a restriction, do not use this page to override it.
If thirst or urine volume has changed
Persistent thirst with high urine volume is worth testing rather than drinking through, since it is a classic early presentation of high blood glucose. The fasting glucose and HbA1c in a medical check up settle that question, and fasting insulin with HOMA-IR shows how hard the body is working to hold glucose steady. To review it with a doctor, book a consultation.
Every iLIV guide is written and reviewed under our editorial standards, and each one carries the name of the reviewing doctor together with their MMC registration number.
