Find Out How Much Water Your Day Really Needs
Enter your weight, training time, and climate to get a daily target and a simple way to spread it out.
This tool was built by Serge (MSc) using general hydration guidance of about 35 ml of fluid per kilogram of body weight, with extra added for exercise and heat. My background is a lifelong natural lifter with over a decade of drug-free training and a science background (MSc).
My tools are for educational purposes and give practical guidance, not professional advice.
Eight glasses a day is a tidy rule, but it ignores the fact that a 55 kg person and a 100 kg person who trains for an hour are not in the same position at all.
This tool starts with your body size, then adds what you lose through training and warm weather, and gives you a figure you can actually plan a day around.
A Starting Point, Not a Rule
I treat a number like this as a place to begin, then I watch two simple signals. Thirst tells me when I need more, and pale yellow urine tells me I am in a good range.
That is also how I recommend using the result. Aim for the figure on most days, and let the signals nudge you up or down, because your needs change with sleep, food, and the day you had.
How the Estimate Is Built
The base amount is 35 ml per kilogram of body weight. Training adds about 10 ml for every minute you exercise, and warm or hot weather raises the total by 10 or 20 percent.
The figure shown is for fluids, so water, tea, coffee, milk, and other drinks all count. Food usually supplies another fifth or so of your total water, which is why the target is lower than the total intake figures you may have seen elsewhere.
Spreading It Across the Day
Drinking it all at once does not work, and chasing it late at night mostly costs you sleep. The table splits your day into sensible parts, with a separate amount for sipping during training.
More is not always better, either. Drinking far beyond thirst for hours at a time can upset your body's salt balance, so use the target as a guide and not a challenge.
Related Tools
Hydration and calories both rise with body size and training, so it helps to check your daily calorie needs alongside this. If you are cutting weight, the calorie deficit calculator is worth a look, since thirst is easy to mistake for hunger.
For long sessions in the heat, the heart rate zone calculator helps you keep your effort at a pace your body can handle.