Water Intake Calculator

Estimate how much water to drink each day based on your weight and activity level, in cups or litres.

100% Browser-Based • Local Processing
Units
kg

Individual needs vary widely. Food contributes roughly a fifth of your fluid, and tea, coffee, milk and juice all count toward the rest. Thirst and pale-straw urine are better day-to-day guides than any formula. Not medical advice.

Suggested daily fluid

2.8 L

Millilitres 2,800 ml
US fluid ounces 95 fl oz
Glasses (250 ml) 11
From drinks alone 2.2 L
Basis and working

The basis

fluid = 35 ml × body weight (kg) + exercise + climate

Your numbers

35 × 70 = 2,450 ml, + 350 ml for 30 minutes of exercise, + 0 ml for a temperate climate = 2,800 ml a day.

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Privacy Focused

🔒 Local Processing. Your numbers never leave your device.

Instant Results

🌐 Fully Client-Side. Runs instantly in your browser.

No Signup

⚡ No accounts. No API keys. Just open and use.

Browser Based

🚀 No installs, no sign-ups, no server round-trip.

Overview

What is a Water Intake Calculator?

A Water Intake Calculator estimates how much water to drink each day based on your body weight and activity level. It gives a daily target in millilitres or ounces and an approximate number of glasses, adjusting up for exercise and hot climates. It's a general guide — your real needs vary — and it runs privately in your browser.

'Drink eight glasses a day' is a one-size-fits-all rule that ignores your size and activity. A weight-based estimate gets you closer to a sensible personal target — more if you're bigger or active, less if you're not.

This calculator gives a daily water figure from your weight and activity, in your preferred units. It runs entirely in your browser, so your details stay private. Treat it as a guide, not a strict rule.

Guide

How to estimate your water intake

Step 1: Enter your weight and choose your units

Enter your weight and choose your units.

Step 2: Select your activity level (and climate, if hot)

Select your activity level (and climate, if hot).

Step 3: Read your estimated daily water target in litres/ounces and glasses

Read your estimated daily water target in litres/ounces and glasses.

Screens

Water Intake Calculator in action

Water Intake Calculator showing a daily water target in the browser.
Daily water target
Daily water estimate in litres and glasses.
Glasses
Estimating water intake on a phone, no app installed.
Mobile (stacked)
Details

How much water you actually need

A common approach bases water on body weight — roughly 30–35 ml per kilogram (about 0.5 oz per pound) per day as a baseline — then adds more for exercise (you lose water through sweat) and hot or dry climates. The calculator uses your weight and activity to produce a target and converts it into glasses for an easy mental picture. But hydration is genuinely individual, and a few honest points keep this realistic: needs vary a lot with body size, sweat rate, health conditions, pregnancy or breastfeeding, and altitude; a large share of your water comes from food (fruits and vegetables especially) and other drinks, not just plain water, so the figure is total fluid, not necessarily extra glasses on top of everything; and more is not always better — drinking excessively can, in rare cases, dilute blood sodium dangerously. The most reliable everyday guide is your own body: pale-yellow urine and not feeling thirsty usually mean you're well hydrated. Use this number as a starting target and adjust to how you feel and what you're doing. It isn't medical advice. Everything computes locally in your browser.

Support

Frequently Asked Questions

How much water should I drink a day?

A weight-based estimate is roughly 30–35 ml per kg of body weight (about half an ounce per pound), adjusted up for exercise and hot weather. For many adults that lands somewhere around 2–3 litres of total fluid. The calculator personalises it to your weight and activity — but individual needs vary.

Does the 'eight glasses a day' rule apply to everyone?

Not really — it's a rough average that ignores body size, activity, and climate. A larger or very active person needs more; a smaller, sedentary person less. A weight-and-activity-based estimate like this one is closer to a personal target than a fixed number of glasses, though both are just guides.

Do other drinks and food count toward my water?

Yes. A significant portion of your daily fluid comes from food — especially fruits and vegetables — and from other beverages like tea, milk, and juice. So the calculator's figure is total fluid intake, not necessarily plain water you must add on top of everything else you consume.

Does exercise change how much I need?

Yes, significantly. You lose water through sweat during exercise, so active people and athletes need more — often substantially more in hot conditions or long sessions. The calculator increases the estimate with your activity level; on heavy-training days, drink to thirst and replace what you sweat out.

Can I drink too much water?

Rarely, but yes — drinking far more than you need over a short time can dilute blood sodium (hyponatremia), which is dangerous. This is uncommon in normal life. The calculator's estimate is a sensible target, not a minimum to force down; spread intake through the day and let thirst and urine colour guide you.

How do I know if I'm well hydrated?

The simplest signs are pale-yellow urine and not feeling thirsty. Dark urine suggests you need more; very frequent clear urine may mean you're drinking more than necessary. These everyday cues are more reliable than hitting an exact number, so use the calculator's figure as a guide and adjust to your body. It isn't medical advice.

Is it free, and do I need to sign up?

Yes, it's completely free with no account, no trial, and no limit on how many times you use it. It runs entirely in your browser, so there's no sign-in wall — just open the page and calculate.

Is my data private?

Yes. Everything is calculated in your browser — the numbers you enter are never sent to a server, and nothing is stored once you close the tab. That keeps any personal figures (salary, loan, health) on your own device.

Does it work on mobile?

Yes. It runs in your phone's browser with nothing to install, so you can calculate on Android or iOS. The layout adapts to small screens, so entering numbers and reading the result is easy on the go.

Does it work offline?

Once the page has loaded, the calculation runs entirely on your device, so it keeps working without a connection. You only need to be online to open the page the first time — which is also why nothing you enter is uploaded.

Can I copy or share the result?

Yes. You can copy the result to your clipboard with one click, and many results can be shared. Because everything is calculated locally, copying is instant with no upload step.

How accurate is it, and is this professional advice?

The math is accurate for the inputs you give, and the formula is shown so you can verify it. But results are estimates for general use, not professional advice — finance calculators use simplified assumptions and ignore fees and rate changes, and health calculators are general estimates, not medical advice. For important decisions, consult a qualified professional.

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