Daily Water Intake Calculator by Weight
Your weight is the single biggest factor in how much water you need. The rule is simple: 35 ml per kilogram of body weight a day, before activity and climate are added on top. That means a 50 kg person needs far less than a 100 kg person, even if they do the same things all day. The daily water intake calculator by weight above works out your number from your weight in kilograms or pounds, plus your exercise, activity and climate.
This page gives you the full chart by weight, shows the maths for kilograms and pounds, and explains how activity, climate and special conditions change the result.
The 35 ml per Kilogram Rule
The calculator’s base is 35 ml of water per kilogram of body weight per day. It is a well-established clinical rule of thumb, used in hospitals to estimate fluid needs. It is not the whole answer — activity, climate and exercise add to it — but it is the foundation, and it scales cleanly with weight. A 50 kg person starts at 1,750 ml; a 100 kg person starts at 3,500 ml. Double the weight, double the base.
Daily Water Intake by Weight (Kilograms)
The table below shows the base and the daily total for a moderately active person with 30 minutes of exercise in a temperate climate, at weights from 50 to 100 kg.
| Weight | Base (× 35 ml) | Daily total | Litres | Fluid ounces |
|---|---|---|---|---|
| 50 kg | 1,750 ml | 2,548 ml | 2.55 L | 86 fl oz |
| 60 kg | 2,100 ml | 2,985 ml | 2.99 L | 101 fl oz |
| 70 kg | 2,450 ml | 3,423 ml | 3.42 L | 116 fl oz |
| 80 kg | 2,800 ml | 3,860 ml | 3.86 L | 131 fl oz |
| 90 kg | 3,150 ml | 4,298 ml | 4.30 L | 145 fl oz |
| 100 kg | 3,500 ml | 4,735 ml | 4.74 L | 160 fl oz |
Check the 60 kg row: base 2,100 ml × 1.25 = 2,625 ml, plus 360 ml for exercise, gives 2,985 ml. And the 90 kg row: 3,150 × 1.25 = 3,937.5, plus 360, gives 4,297.5, rounded to 4,298 ml. Every 10 kg of weight adds about 438 ml to the daily total at this activity level.
Daily Water Intake by Weight (Pounds)
If you weigh yourself in pounds, the calculator converts first: divide pounds by 2.205 to get kilograms. A person at 154 lb weighs 69.9 kg, so their base is 69.9 × 35 = 2,445 ml, and their daily total at moderate activity with 30 minutes of exercise is 3,416 ml — 3.42 litres, or 116 fluid ounces. The table below shows common pound weights and their totals at the same activity level.
| Weight | Weight in kg | Daily total | Fluid ounces |
|---|---|---|---|
| 110 lb | 49.9 kg | 2,543 ml | 86 fl oz |
| 132 lb | 59.9 kg | 2,979 ml | 101 fl oz |
| 154 lb | 69.9 kg | 3,416 ml | 116 fl oz |
| 176 lb | 79.8 kg | 3,853 ml | 130 fl oz |
| 198 lb | 89.8 kg | 4,289 ml | 145 fl oz |
| 220 lb | 99.8 kg | 4,726 ml | 160 fl oz |
Check the 176 lb row: 176 ÷ 2.205 = 79.8 kg, base 79.8 × 35 = 2,794 ml, × 1.25 = 3,492 ml, plus 360 ml, gives 3,852 ml — the table says 3,853 ml, the one-millilitre difference coming from rounding the kilogram conversion. Use the calculator above for your exact weight rather than rounding from a table.
How Activity Changes the Number
Weight sets the base, but activity multiplies it. The table below shows the daily total for a 70 kg person with 30 minutes of exercise, at each activity level and in a temperate climate.
| Activity level | Multiplier | Daily total (70 kg) |
|---|---|---|
| Sedentary | 1.00 | 2,810 ml |
| Lightly active | 1.15 | 3,178 ml |
| Moderately active | 1.25 | 3,423 ml |
| Very active / athlete | 1.40 | 3,790 ml |
The gap between sedentary and very active is 980 ml a day for the same person — more than a litre. And exercise adds on top: the 30 minutes in these figures already adds 360 ml, so a very active person who trains for an hour adds 720 ml instead, taking the total to 4,150 ml. If you train hard, your water needs rise fast.
Climate and Special Conditions
Climate multiplies the base too: cold weather adds 5%, hot and humid adds 10%, and hot and dry adds 15%. A 70 kg moderately active person with 30 minutes of exercise needs 3,423 ml in a temperate climate, 3,576 ml in the cold, 3,729 ml when hot and humid, and 3,882 ml when hot and dry. Pregnancy adds a flat 300 ml and breastfeeding adds 700 ml on top of everything else — so the same person breastfeeding needs 4,123 ml a day. The calculator has a dropdown for these conditions, and it applies the adjustment automatically.
When Weight Changes, So Does Your Target
Your water target moves with your weight. Lose 10 kg and your base falls by 350 ml; gain 10 kg and it rises by the same amount. If you are actively losing weight, recalculate your target every 5 kg, just as you would recalculate your calories. The calorie calculator works the same way — both numbers are built from your weight, so they move together. And if you are tracking your weight, your BMI tells you which category your weight sits in.
Children and Older Adults
The 35 ml rule is for adults. Children need water by a different rule — roughly 100 ml per kg for the first 10 kg, 50 ml per kg for the next 10 kg, and 20 ml per kg after that — and their needs should be checked with a paediatrician. Older adults often feel less thirsty even when they need water, so they should drink on a schedule rather than waiting for thirst. If you care for an older person, a glass of water with every meal and one between meals is a good routine.
Tracking Your Intake
- Work out your target with the calculator above and note it in litres and bottles.
- Pick a bottle size — half-litre bottles make the maths easy: our 70 kg example needs 6.8 of them.
- Fill the bottles in the morning so you can see the day’s target.
- Drink one bottle before lunch, two by mid-afternoon, and the rest by dinner.
- Check your urine colour in the afternoon: pale yellow means you are on track.
- Recalculate whenever your weight, activity or the season changes.
Related tools: your energy plan from the calorie calculator and your TDEE calculator, and your BMI for the weight behind the number. The Mayo Clinic explains how much water you need and what counts toward it.
Key Takeaways
Use the water intake calculator above with your own numbers, and keep the reference figures below handy while you plan.
| Person | Daily total | Fluid ounces | 8-oz glasses |
|---|---|---|---|
| 50 kg, sedentary | 1,750 ml | 59 fl oz | 7.4 glasses |
| 70 kg, moderately active | 3,423 ml | 116 fl oz | 14.5 glasses |
| 90 kg, moderately active | 4,298 ml | 145 fl oz | 18.2 glasses |
| 70 kg, pregnant | 3,723 ml | 126 fl oz | 15.7 glasses |
| 70 kg, breastfeeding | 4,123 ml | 139 fl oz | 17.4 glasses |
What to remember
- Your base is 35 ml per kilogram of body weight a day, before activity and climate.
- A 70 kg moderately active person needs about 3.42 litres a day; a 50 kg sedentary person about 1.75 litres.
- About 20 percent of daily water comes from food — the rest must be drunk.
- Exercise adds 12 ml per minute on top of your base intake.
- Pale yellow urine in the afternoon is the simplest sign you are drinking enough.
Your checklist
- Enter your weight, exercise, activity level and climate in the calculator above.
- Note your target in litres, ounces, glasses and bottles.
- Fill your bottles in the morning so you can see the day target.
- Drink a glass with every meal and one between meals.
- Recalculate whenever your weight, activity or the season changes.
Mistakes to avoid
- Trusting the eight-glass rule — it is a minimum for a small sedentary person, not a target.
- Waiting for thirst, which is a late signal, not an early one.
- Forgetting that food counts — fruit, soup and yoghurt all contribute.
- Counting alcohol as hydration — it dehydrates rather than hydrating.
- Drinking far more than you need, which can dilute blood sodium.
Frequently Asked Questions
How much water should I drink per kg of body weight?
About 35 ml per kilogram a day as a base, before activity and climate. A 70 kg person starts at 2,450 ml; a 90 kg person at 3,150 ml. Add activity, climate and exercise on top — the calculator above does the full calculation.
How much water should a 70 kg person drink a day?
About 3.42 litres if moderately active with 30 minutes of exercise, in a temperate climate. Sedentary, the same person needs 2.81 litres; very active, 3.79 litres. The base alone is 2.45 litres.
How much water should a 154 lb person drink a day?
154 lb is 69.9 kg, so the base is 2,445 ml and the daily total at moderate activity with 30 minutes of exercise is 3,416 ml — 3.42 litres or 116 fluid ounces.
Does my water intake change if I lose weight?
Yes. Every 10 kg of weight changes your base by 350 ml a day. Lose 10 kg and your target falls by roughly 440 ml at moderate activity. Recalculate your target every 5 kg lost, just as you would your calories.
How much water do I need if I exercise every day?
Add 12 ml for every minute of exercise, on top of your activity multiplier. An hour of exercise adds 720 ml. In hot conditions you may need more, because sweat losses rise sharply with temperature.
Is the 35 ml per kg rule the same for everyone?
It is a starting point for healthy adults. Older adults, people with kidney or heart conditions, and anyone on medicines that affect fluid balance should follow their doctor’s guidance instead. Children use a different rule entirely.
Disclaimer: This calculator provides estimates for general information only and is not medical advice. Water needs vary with health conditions, medicines, pregnancy and climate. Consult a doctor if you have kidney disease, heart failure, or any condition that affects fluid balance.