How Much Water Should I Drink Based on My Weight?

Why the calculator starts with your weight

A larger body usually needs more fluid. The calculator starts with a range of millilitres per kilogram, then adjusts it for the kind of day you’re planning. Think about what you’ll eat and drink, how much you’ll sweat and whether you’ve been given your own fluid advice.

Try changing the weight to see how the range moves. The estimate is for your daily fluids, which can include drinks such as tea, coffee and milk. See how the calculator works if you want to check the maths behind the result.

Calculate a basic weight-based estimate

Convert pounds to kilograms, when necessary, by multiplying pounds by approximately 0.4536. HydrateWise then uses roughly 31 to 35 millilitres per kilogram, matching the published methodology. At 70 kilograms, that broad starting range is about 2,170 to 2,450 millilitres. It is deliberately a range rather than a precise biological requirement. The apparent accuracy of a number such as 2,347 ml should not be confused with certainty.

The calculator expresses the result in litres, millilitres and cup equivalents so you can use the unit that fits your routine. Cup sizes differ, which is why millilitres are clearest. A 500 ml bottle is easier to count than an abstract litre target: a 2.5 litre estimate is five standard bottles across the day, including equivalent fluids from other drinks.

Adjust for what you’re doing today

Exercise increases fluid loss through sweat and breathing. Effort, time, clothing and the weather all play a part. Choose the activity that fits today, whether that’s a short strength session in a cool gym or a long run in humid weather.

For longer or repeated sessions, weigh yourself before and after a similar workout and note what you drank. That can help you estimate sweat loss. If you sweat heavily or train in the heat, ask a qualified professional whether your plan needs to account for sodium as well as fluid.

Climate, food and other drinks matter

Hot and humid conditions can increase sweating, while altitude and heated indoor air can also change intake. HydrateWise applies a broad climate adjustment, but weather changes within a day. Recalculate when a heatwave, travel or outdoor work makes the original assumptions obsolete. Thirst and urine patterns offer context, although neither is a perfect diagnostic tool.

Food contributes water. Fruit, vegetables, yoghurt, soup and cooked grains can provide meaningful fluid. Tea, coffee and milk also contribute for most people. Interpret a calculator target as total fluid planning, not an instruction to add the full amount as plain water on top of a moisture-rich diet.

Avoid catching up too quickly

Too much water can be harmful when consumed faster than the body can excrete it because sodium in the blood may become dangerously diluted. Do not treat the estimate as a challenge or catch up by drinking a very large volume quickly. Spread ordinary intake through the day and seek urgent help for severe confusion, seizures, collapse or other concerning symptoms.

A missed morning target does not create a debt that must be cleared immediately. Move some fluid earlier on future days and choose serving sizes that feel comfortable. The planner can show a gentle hourly average, but it is a convenience rather than an instruction to drink continuously.

Turn the estimate into a routine

Fit drinks around things you already do, such as getting up, eating lunch or taking a break. When you know your target, use the bottle and refill planner to work out how many fills you need with your usual bottle.

Review the estimate when circumstances change. A rest day, a long workout and a hot travel day should not share one automatic target. If you regularly feel unusually thirsty, urinate excessively or experience persistent symptoms, speak to a qualified healthcare professional rather than repeatedly increasing the calculator setting.

HydrateWise provides educational planning estimates, not medical advice. Kidney, heart and liver conditions, pregnancy, illness and some medicines can change safe fluid intake. Follow personal clinical guidance where it applies.