Daily Water Intake Calculator

Most water targets ignore the two things that move the number most: how much you train and how hot it is. This one does not. Enter your body weight, the training hours on your plate today, and the heat, and the calculator returns a daily intake target in litres and millilitres. A rest day and a long hot session day pull different amounts.

How the number is built

The base figure comes from your body weight, at roughly 33 ml per kilo. A 70 kg athlete starts around 2.3 litres on a quiet day. Training adds about 750 ml for every hour you spend working, since you lose fluid through sweat and breath the whole time. Heat stacks on top: a warm day adds 500 ml, a hot one adds a litre.

Those three pieces are what you see broken out in the result. The body-weight base stays fixed day to day. The training and heat lines are what swing your total, which is why a calculator that asks about both beats a flat "drink eight glasses" rule.

Daily intake is not session fluid

This tool answers one question: how much total water across the whole day. It does not tell you how much to drink mid-run or mid-ride. Sweat rate varies by person, pace and conditions, and during a hard session you can lose more than a litre an hour, far past any daily average.

For the during-session figure, measure your actual loss with the sweat rate calculator. Use this page to set the daily total and that one to plan what goes in your bottles. If you are fuelling a race, the race nutrition calculator ties carbs and fluid together for the event itself.

Reading the result

Treat the total as a target to hit across waking hours, not a glass to down at once. Spread it out, lean earlier in the day, and back off in the last hour before sleep. Urine that runs pale through the day is the simplest check that you are landing in range.

Body size, salt loss and climate all shift the real need, so use the number as a starting point and adjust by how you feel and perform. For a fuller routine on tracking fluid alongside Garmin and Apple Health data, read the hydration tracking guide.