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Nutrition

Water intake calculator

A daily hydration range based on bodyweight, training, and climate — not a single number you have to hit.

Your stats

Daily water target
3.0–5.7litres

Roughly 102–192 fluid ounces per day, including water from food.

Range (ml)
3016–5678ml
Range (oz)
102–192fl oz

Thirst is a better real-time signal than any formula. Use this as a ballpark, not a target you have to hit on a hot day at the same number as a sedentary one.

How much water you actually need

The Institute of Medicine puts adequate daily total water intake at around 3.7 litres for adult men and 2.7 litres for adult women, including water from food (which covers roughly 20 percent of intake for a typical diet). Training and heat raise the requirement; sedentary days in a cool climate lower it.

The number on this page is a range, not a target. Anywhere inside it is fine. Most people get into trouble at the bottom of the range, not the top.

How it is calculated

min oz = weight(lb) × 0.5 + activity adj + climate adj
max oz = weight(lb) × 1.0 + activity adj + climate adj

activity adj: low 0, moderate +12 oz, high +20 oz
climate  adj: temperate 0, warm +8 oz, hot +16 oz

Ounces are converted to millilitres and litres at 29.57 ml per US fluid ounce.

Frequently asked questions

Where does the 'half your bodyweight in ounces' rule come from?
It is a long-standing rule of thumb used by dietitians and trainers — drink half your bodyweight (in pounds) in fluid ounces per day, with extra for training and heat. The exact origin is unclear, but it lines up with the Institute of Medicine's adequate-intake figures of about 2.7 L for women and 3.7 L for men, including water from food.
Does coffee count?
Yes. The old claim that caffeine has a meaningful diuretic effect doesn't hold up — at habitual intakes (say, 1–4 cups a day), coffee and tea contribute to daily hydration about as well as water. Alcohol is genuinely dehydrating; everything else with water in it counts.
Should I really drink to a number?
Not strictly. Thirst is a reliable signal in healthy adults. The numbers here are best used to check whether your usual intake is in the ballpark — most people undershoot rather than overshoot. If your urine is pale yellow most of the day, you're roughly on track.
Can you drink too much water?
Yes, although it is rare in normal circumstances. Drinking very large volumes (multiple litres in a couple of hours) can dilute blood sodium and cause hyponatraemia. Risk is higher in endurance events where athletes drink heavily without replacing electrolytes. Spread intake across the day and add a little salt when you sweat hard.

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