How much water should you drink a day?
Your daily target from weight, activity, climate and altitude — shown in ounces, millilitres, litres, cups and bottles at once.
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Used only to show the matching adequate-intake reference figure.
Moderate to vigorous exercise — the kind that makes you sweat.
Your daily target
119oz
- Millilitres
- 3,525 mL
- Litres
- 3.5 L
- 8 oz cups
- 14.9
- Your bottles
- 7.1
Two answers, and why they differ
- Bodyweight rule (what most calculators use)
- 119 oz
- NASEM adequate intake, from drinks
- 73 oz
These disagree by more than 20%. The bodyweight rule is a rule of thumb with no strong evidence behind it; the NASEM figure comes from population data and assumes about a fifth of your water comes from food. Treat the range between them as your target, not either number as a rule.
Where it comes from
- Base, from bodyweight107 oz
- 30 min of activity+12 oz
That is about 14.9 glasses of water, or 7.1 of your bottle.
How much water should you actually drink a day?
The honest answer is that there is no single number, and any calculator that gives you one without caveats is overselling its own precision. The most widely cited reference figures come from the US National Academies (NASEM, formerly the IOM): about 3.7 litres of total water a day for men and 2.7 litres for women. Total water includes what you get from food, which is roughly 20% of intake — so the amount you need to actually drink is closer to 3.0 and 2.2 litres.
The other common approach, and the one nearly every calculator on the first page of Google quietly uses, is two thirds of your bodyweight in ounces. It is easy to compute and it produces sensible-looking numbers for average adults. It also has no strong evidence base. This page shows you both, because the gap between them is more informative than either one alone.
What actually changes your needs
- Exercise. Roughly 350–500 mL (12–16 oz) extra per 30 minutes of hard effort, and much more in heat. If you want a real number rather than an estimate, weigh yourself before and after a session — that is what the sweat rate calculator does.
- Heat and humidity. Humidity matters more than most people expect, because sweat that cannot evaporate does not cool you, so you keep producing more of it.
- Altitude. Above about 2,500 m you lose more water through breathing and increased urine output — roughly a litre a day.
- Health and medication. Kidney conditions, heart failure, diuretics and pregnancy all change fluid needs, sometimes in the direction of drinking less. This is the point where a calculator stops being useful and a clinician starts.
Does coffee count?
Mostly, yes. The diuretic effect of caffeine at normal doses is small enough that tea and coffee still contribute net fluid. They are not water, but they are not a hydration debt either.
A better signal than any calculator
Pale straw-coloured urine and an absence of thirst tell you more about your hydration than arithmetic based on your bodyweight ever will. Use the number here as a starting target, then let your body correct it.
Related tools
- Bottles in a gallonAny bottle size, any volume, US or Imperial gallons — with the whole table laid out so you can just read the answer.
- Printable water trackerBuild a daily, weekly or monthly water tracking sheet, then print it or save it as an image.
- Hydration colour chartTap the shade that matches. Get a plain reading and how much to drink to correct it.
- Sweat rate calculatorWeigh in, train, weigh out. Get your litres-per-hour, your fluid deficit, and how much to drink per hour next time.
These tools give general wellness estimates only. They are not medical advice, diagnosis, or treatment. Fluid needs vary with health conditions and medication — talk to a clinician about yours.
Keep the number
You just worked out your number. Water Goose is where it stops being a number and starts being a habit.