Water Intake by Weight: A Simple Table for Your Body

“Drink 8 glasses a day” doesn’t know if you weigh 110 pounds or 250. That’s the whole problem with a flat number.

Weight is a much better starting variable. Here’s the formula, and a full table so you don’t have to do the math yourself.

The formula

The rule of thumb WaterDrop uses to suggest a starting daily goal is roughly 35 ml per kg of body weight, adjusted a little by activity level. That’s it. No spreadsheet, no app subscription required to know your baseline.

It’s a starting point, not a prescription. Bigger bodies generally need more water, but activity, climate and how much caffeine or alcohol you drink all shift the number too.

Water intake by weight, in full

Here’s 35 ml/kg run out across common adult body weights, converted to both US and UK fluid ounces.

Weight (kg)	Weight (lb)	Daily target (ml)	US fl oz	UK fl oz
50 kg	110 lb	1,750 ml	59.2 oz	61.6 oz
55 kg	121 lb	1,925 ml	65.1 oz	67.8 oz
60 kg	132 lb	2,100 ml	71.0 oz	73.9 oz
65 kg	143 lb	2,275 ml	76.9 oz	80.1 oz
70 kg	154 lb	2,450 ml	82.9 oz	86.2 oz
75 kg	165 lb	2,625 ml	88.8 oz	92.4 oz
80 kg	176 lb	2,800 ml	94.7 oz	98.6 oz
90 kg	198 lb	3,150 ml	106.5 oz	110.9 oz
100 kg	220 lb	3,500 ml	118.4 oz	123.2 oz

Find your rough weight, that’s your starting daily target. Round it to whatever’s easiest to track.

Why US and UK ounces are both in the table

A US fluid ounce is 29.57 ml. A UK fluid ounce is 28.41 ml. They’re close enough to look interchangeable and different enough that using the wrong one quietly shifts your goal by several ounces. Most hydration content on the internet just says “oz” and never tells you which one. I go deep on that mix-up in ml to oz water conversion, which is worth reading if you’ve ever wondered why two “68 oz” goals from different apps didn’t match.

Adjusting the baseline

The table above is a starting point for an averagely active day. A few things push it up, without needing exact numbers attached:

• A hard workout or heavy sweating means drinking more than your baseline that day.
• Hot or dry climates pull more water out of you than a cool, humid one.
• Coffee, tea, alcohol and other drinks all count differently toward your total, not at a flat 100%.

None of this needs to be perfectly calculated daily. It needs to be a rough habit: know your baseline, drink more when it’s clearly warranted, and don’t stress about the exact ounce.

Weight also isn’t fixed, which is easy to forget. If you lose or gain a noticeable amount over a few months, your baseline shifts with it. Nobody needs to recalculate weekly, but checking your target against the table above every so often keeps it from going stale.

How this compares to the flat rules

The 8x8 rule gives everyone 64 US oz, regardless of weight. Look at the table above and you’ll see that number only roughly matches someone around 55-60 kg. Above that, 8x8 quietly undershoots. I went through exactly where that flat rule came from in the 8 glasses of water a day myth.

On the other end, the gallon-a-day trend (128 US oz) overshoots the weight-based target for almost everyone under 100 kg, sometimes by a lot. That comparison is broken down in gallon of water a day.

Weight-based sits between those two extremes, which is the point. It’s not designed to be a bigger or smaller number, it’s designed to actually be about you.

This is not medical advice

35 ml per kg is a rule of thumb, not a diagnosis or a treatment plan. It’s the same starting-point logic the WaterDrop app uses to suggest a goal, and it’s meant to be adjusted, not memorized as gospel. If you have a kidney condition, heart condition, are pregnant, or have any reason to think your fluid needs are unusual, your body and your doctor know more than a table on a blog.

FAQ

How much water should I drink based on my weight? Roughly 35 ml per kg of body weight as a starting point, adjusted a little for activity level. Use the table above to find your rough number in ml, US oz and UK oz.

Does this formula work the same for everyone? It’s a general starting point for adults, not personalized medical guidance. Pregnancy, certain health conditions and extreme activity levels can all shift what’s appropriate, which is a conversation for your doctor, not a blog table.

Why does the table show both US and UK ounces? Because they’re different units (29.57 ml vs 28.41 ml) and most sources don’t specify which one they mean. Using the wrong one can throw your daily number off by several ounces.

Is a higher body weight always a higher water need? Generally yes as a baseline, but activity level and climate can matter just as much. A smaller, highly active person can need more than a larger, sedentary one.

Related reads:

• Daily Water Intake Calculator, the broader formula, activity and climate included
• How Many Ounces of Water a Day, full oz conversion table for common goals
• The 8 Glasses of Water a Day Myth, why the flat number falls short
• ml to oz Water Conversion, the US vs UK ounce trap in full

Sources

• Institute of Medicine — Dietary Reference Intakes for Water
• Harvard T.H. Chan School of Public Health — The Nutrition Source: Water

This article is general information, not medical advice. Talk to a qualified professional about anything affecting your health.

— Dolce