Water Intake Calculator
How much water you need in a day, adjusted for what you weigh, how hard you train and where you live.
Where it comes from
| Source | Ounces |
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How to spread it
| When | Amount |
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The baseline is roughly half an ounce of water per pound of body weight, with extra added for training time, sweat rate, heat and diuretics. Food contributes about twenty percent of most people’s total fluid, which is accounted for in the breakdown. Urine the colour of pale straw is the practical check — clear all day usually means you are overdoing it. General fitness information, not medical advice.
How much water should you drink a day?
The eight-glasses rule came from nowhere in particular and ignores the two things that matter most: how big you are and how much you sweat. A 130-pound office worker and a 250-pound lifter training in a hot gym do not need the same amount of water, and pretending they do is why most people get this wrong in both directions.
The baseline
Start at roughly half an ounce of water per pound of body weight. For a 190-pound man that is about 95 ounces, or just under three litres. Then add for the things that pull fluid out: training time, how heavily you sweat, heat and humidity, and caffeine or alcohol. About twenty percent of your total fluid arrives through food, which this calculator subtracts so the number you see is water you actually have to drink.
What dehydration costs you in the gym
Losing two percent of body weight in fluid is enough to measurably reduce strength, endurance and focus. For a 190-pound man that is under four pounds — which is an ordinary hot session without a bottle. If your performance falls off a cliff in the back half of a workout and your food and sleep are fine, water is the first thing to check.
How to actually hit it
Nobody drinks three litres by remembering to. Attach it to things you already do: a glass on waking, one before training, a bottle during, one with each meal. The calculator above splits the day for you. A marked bottle you fill a known number of times beats any app.
The colour check
Pale straw is the target. Dark yellow means you are behind. Completely clear all day usually means you are drinking more than you need and flushing sodium with it, which is its own problem for anyone training hard — especially on a low-carb diet, where sodium and water both run low.
Common questions
Does coffee count? Mostly yes. The diuretic effect is mild and partially offset by the fluid itself. The calculator adds a small correction for heavy intake rather than discounting it entirely.
Can you drink too much? Yes, though it is rare. Drinking several litres in a short window while losing sodium through sweat is genuinely dangerous. Spread it across the day.
Do I need electrolytes? If you sweat heavily, train over an hour, or eat low-carb, adding sodium to your water helps more than adding more water.
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