Signs you're dehydrated
Dark yellow urine, headache, dry mouth, fatigue and dizziness are early signals. Thirst itself is a lagging indicator — especially in older adults, whose thirst response weakens with age — so don't wait for it.
Drink this much today
2.4litres
A sensible range is 2.2–2.6 L of fluids, on top of 0.5 L you will get from food.
0% logged
Why this number?
| Baseline for your body & age70 kg × 35 ml/kg (age 30) | +2.45 L |
| Sweat replacement30 min moderate · 0.65 L/hr | +0.33 L |
| Climate loadTemperate conditions, average air | +0.10 L |
| Water you get from foodAbout 20% of baseline needs arrive via meals | −0.49 L |
| Your daily drinking target | 2.39 L |
This calculator provides general educational estimates and is not medical advice. Individual needs vary. Speak to a doctor before making changes if you are pregnant, or have kidney, heart or liver conditions, or take medication affecting fluid balance. See the full methodology and sources.
Your drinking schedule
- 7:00 AM440 ml
- 9:00 AM320 ml
- 11:00 AM320 ml
- 1:00 PM320 ml
- 3:00 PM320 ml
- 5:00 PM270 ml
- 7:00 PM190 ml
- 9:00 PM190 ml
Log what you have drunk
Not all drinks hydrate equally. Coffee and tea still count; alcohol works against you.
- Water250 ml · 100% as hydrating as water0
- Coffee240 ml · 85% as hydrating as water0
- Tea240 ml · 90% as hydrating as water0
- Milk250 ml · 110% as hydrating as water0
- Juice200 ml · 95% as hydrating as water0
- Soda330 ml · 85% as hydrating as water0
- Sports drink500 ml · 100% as hydrating as water0
- Beer330 ml · 40% as hydrating as water0
- Wine150 ml · net water loss0
Log a drink to see how you are tracking against today's target.
Free · No sign-up · Updates instantly
Water Intake Calculator: how much should you drink?
Not a generic 8-glasses rule. Your weight, exercise, climate, altitude and life stage all change what your body needs — see the full maths, then get an hourly plan for the rest of your day.
- Live result, no "Calculate" button
- Full breakdown of every input
- Personal hourly drinking schedule
- Optional beverage log with real coefficients
Estimates draw on EFSA Dietary Reference Values and U.S. National Academies intake references. Read the methodology →
Hydration by lifestyle
Office workers often under-drink simply from being seated and distracted; keeping a bottle at your desk and refilling on a schedule beats trying to remember. Athletes should weigh in before/after training — every kg lost is roughly 1 L of sweat.
Can you drink too much?
Yes — water intoxication (hyponatraemia) is real but rare outside endurance sport or compulsive over-drinking. Spreading intake across the day, as the schedule above does, is safer than large boluses.
The complete guide
Water intake calculator: everything you need to know
A water intake calculator is a tool that works out how much water you should drink each day, based on personal factors — weight, age, sex, activity level and climate — rather than a one-size-fits-all rule. The "drink 8 glasses a day" guideline that most of us grew up with was never based on strong individual evidence; it is a reasonable population average, but a 55 kg office worker in a cool climate and a 95 kg construction worker in summer heat do not need the same amount of water. Our daily water intake calculator asks for the inputs that actually change your number, then shows the maths behind the result instead of hiding it.
How does a daily water intake calculator work?
Enter your weight, age, sex, how much you exercised today, the climate you're in and (optionally) altitude or pregnancy/breastfeeding status. The calculator combines these into a baseline figure per kilogram of body weight, then adds litres for sweat losses from exercise, heat and humidity, and altitude, before subtracting the water you typically get from food. The result updates live as you change any input — there's no "Calculate" button to click, and every term in the sum is shown in the "Why this number?" panel so you can see exactly where your target comes from.
Water intake calculator by weight (kg and litres)
Body weight is the single biggest driver of your target — heavier people carry more total body water and need proportionally more to replace it. As a rough guide, most adults need somewhere around 30–35 ml of water per kilogram of body weight per day before other adjustments. On our water intake calculator by weight, a 60 kg adult typically lands around 1.8–2.3 litres a day, while a 90 kg adult lands closer to 2.6–3.1 litres. For the full kg-to-litre reference table, see our water intake chart by weight and age.
Water intake calculator by age
Water needs per kilogram are highest in childhood and adolescence and decline gradually with age, partly because the kidneys' concentrating ability and the sensation of thirst both weaken over time. Our calculator uses a different millilitres-per-kilogram figure for each age band — from children through to adults over 65 — rather than treating a 25-year-old and a 70-year-old the same. Older adults in particular should not rely on feeling thirsty as a signal; scheduled drinking, like the hourly plan the calculator generates, is a more reliable habit.
What's a "recommended," "optimal" or "required" water intake?
There is no single ideal, optimal or required water intake figure that applies to everyone — suggested intakes from major health bodies span a range because individual needs genuinely vary. The EFSA (European) reference is 2.0 litres/day total water for women and 2.5 litres/day for men; the U.S. National Academies figure is higher, at 2.7 litres/day (about 11.5 cups) for women and 3.7 litres/day (about 15.5 cups) for men. Both include water from food as well as drinks. Rather than picking one authority's number, our calculator builds your own figure from your actual weight, activity and environment, then shows it as a sensible range (roughly ±8%) instead of a falsely precise single decimal.
Daily water intake calculator for women
Because average body composition and body size differ, reference intakes for women are typically somewhat lower than for men — though individual variation means many women need more than the average man, and vice versa. Our water intake calculator for women also accounts for pregnancy and breastfeeding: EFSA guidance recommends an additional 300 ml/day during pregnancy and 700 ml/day while breastfeeding, both of which are added automatically when you select your status.
Water intake calculator for weight loss
Drinking water will not directly burn fat, but adequate hydration supports several things that matter for weight management: it can blunt appetite when thirst is mistaken for hunger, supports a slightly higher resting energy expenditure in some studies, and replacing sugary or high-calorie drinks with water is one of the more reliable ways to cut calories without noticing. If you're using a water intake calculator for weight loss, use the exercise fields to reflect any extra activity from your plan — a higher activity level raises your target, since sweat losses still need replacing regardless of your goal.
Bodybuilding and creatine: water intake for lifters
A bodybuilding water intake calculator needs to account for training volume, since sweat losses during resistance training can be substantial even without much cardiovascular exertion. Set your exercise minutes and intensity to match your actual session, not just its duration — a dense 45-minute lifting session can lose as much fluid as an hour of light cardio. If you supplement with creatine, it draws additional water into muscle cells and adds a little extra work for your kidneys, which is why more fluid is commonly recommended — switch the calculator above to "Taking Creatine" mode and enter your dose and phase (loading vs. maintenance) for an adjusted target, shown alongside your standard number so you can see exactly how much extra it's adding.
How does this compare to NHS or Mayo Clinic guidance?
The NHS Eatwell Guide recommends around 6 to 8 glasses (roughly 1.5–2 litres) of fluid a day in the UK, in addition to the water you get from food — a similar starting point to the EFSA figures above. Patient-facing guidance from sources like the Mayo Clinic typically points to the same U.S. National Academies reference values cited above (about 11.5 cups/day for women, 15.5 cups/day for men, from all fluids). Unlike a flat NHS or Mayo Clinic water intake calculator figure, ours adjusts that baseline for your actual weight, exercise and the climate you're in, which matters more the further your circumstances sit from "average adult, temperate climate, low activity".
A water intake calculator app — without the app
You don't need to search an app store for a water intake calculator app: this tool runs entirely in your browser, on your phone, tablet or desktop, and behaves like one — your inputs and drink log are saved locally so it remembers you next time, with no account, no download and no permissions to grant. Bookmark the page or add it to your home screen for one-tap access.
Frequently asked questions
What is a water intake calculator and how does it work?
A water intake calculator is a tool that estimates how much water you should drink each day from inputs like your weight, age, sex, activity level and climate, instead of relying on a generic rule like "8 glasses a day". Ours updates live as you adjust the inputs and shows a full breakdown of how the number was reached.
How much water should I drink a day?
Most healthy adults need roughly 2–3.7 litres of total water a day, including food. The calculator above adjusts a personal figure for your weight, age, sex, exercise, climate and altitude rather than giving you a single generic number.
How do I calculate my daily water intake based on my weight?
A common starting point is roughly 30–35 ml per kilogram of body weight per day for an average adult, then adjusted upward for exercise, hot climates, altitude, and pregnancy or breastfeeding, and downward slightly for the water you already get from food. The calculator above runs this calculation automatically and shows each adjustment separately.
How much water should a 70 kg person drink in a day?
A sedentary 70 kg adult in a temperate climate needs roughly 2.1–2.5 litres of drinking water a day; with 45 minutes of daily moderate exercise that rises to around 2.5–2.9 litres. See more reference figures by weight on our water intake chart, or enter 70 kg into the calculator above for a number that also accounts for your age, sex and activity.
Is 2 litres of water a day enough for a man?
It can be for a smaller or sedentary man in a cool climate, but the commonly cited reference intakes for men are higher — 2.5 litres total water a day (EFSA) to 3.7 litres (U.S. National Academies). Larger, more active men, or those in hot climates, typically need more than 2 litres of drinking water alone, so it is worth calculating a figure based on your own weight and activity rather than using a flat number.
How many litres of water should I drink daily?
Most healthy adults should drink somewhere between about 1.5 and 3.7 litres a day, depending on body weight, sex, activity level and climate — there is no single correct number for everyone. Enter your details into the calculator above for a litres (or ounces) target specific to you.
Does coffee and tea count toward water intake?
Yes, mostly. Moderate caffeine intake has a mild diuretic effect, but the fluid volume you consume still counts — coffee and tea are roughly 85–90% as hydrating as plain water.
Can I drink too much water?
Yes — drinking far beyond your needs in a short period can dilute blood sodium (hyponatraemia), which is dangerous. This is rare from normal drinking habits but a real risk during endurance exercise without electrolyte replacement.
Do I need more water when pregnant or breastfeeding?
Yes. EFSA guidance adds about 300 ml/day in pregnancy and 700 ml/day while breastfeeding, which this calculator includes automatically when you select your status.
How does this compare to the Mayo Clinic water intake recommendation?
Patient-facing guidance from sources like the Mayo Clinic typically points to the same U.S. National Academies reference values we cite: roughly 11.5 cups (2.7 L) of total fluids a day for women and 15.5 cups (3.7 L) for men. We are not affiliated with the Mayo Clinic — we simply use the same widely-cited baseline, then personalize it to your weight, activity, climate and altitude instead of leaving it as one flat figure.
Is there a water intake chart showing how much I should drink per day?
Yes — our water intake chart lists daily targets broken down by body weight (50–120 kg / 110–265 lb) and by age group, for both sedentary and active people. It is a quick reference; the calculator above gives a more precise figure for your exact situation.
How much extra water should I drink when taking creatine?
Commonly-cited guidance is roughly an extra 250–500 ml (about 8–16 fl oz) a day on top of your normal target, since creatine draws additional water into muscle cells and adds a small extra load for your kidneys to process. Switch the calculator above to "Taking Creatine" mode, enter your dose and phase, and it will show this adjustment on top of your personal baseline rather than a flat number.
Does creatine loading phase require more water than maintenance?
Generally yes. A loading phase (~20 g/day, usually split into several doses) involves a much larger daily amount of creatine than maintenance (~3–5 g/day), so the commonly recommended extra fluid sits toward the top of the 250–500 ml range during loading, versus the lower end during maintenance. The calculator's "Taking Creatine" mode scales the adjustment by both your dose and phase.
Does this work as a water intake calculator app for my phone?
It is a free web tool that works like an app on any phone, tablet or desktop browser — no download or install needed. Your inputs and drink log are saved on your device, so it remembers you between visits.
Is this a water intake calculator for cats or other pets?
No — this tool is calibrated for human physiology only and should not be used to estimate a pet's water needs. Cats and dogs have different requirements (roughly 50–60 ml/kg/day for cats, and it varies further with diet); ask your vet for guidance.
More questions? Visit the full FAQ page.