Free Water Intake Calculator (+ Guide)

What is a water intake calculator?

A water intake calculator estimates how much to drink in a day. It starts from a base for your sex and adds what exercise and heat take out through sweat.

The base comes from the US National Academies' 2004 report on water.

It found adequately hydrated women take in about 2.7 L of total water a day and men about 3.7 L, with about 80% from drinks and 20% from food.

How to use the water intake calculator

You only need your sex and today's exercise.

Your numbers stay in this browser.

A worked example

Here's the example the calculator loads when you press Try an example.

A man trains for an hour on a hot day. His base is about 3.0 L from drinks, and the hour adds 0.8 L, the top of the American College of Sports Medicine's range for heat.

That's about 3.8 L a day, or 15 glasses of 250 ml. On a rest day in mild weather, his base of 3.0 L is enough.

How much exercise adds

Sweat losses vary a lot between people, so the calculator uses the middle of the range, or the top in heat.

For long sessions, weigh yourself before and after: each kg lost is about a liter of sweat to replace.

How to tell if you're drinking enough

Your body gives you clear signs, and they beat any formula.

The color of your pee

Pale yellow means you're well hydrated. Dark yellow means drink more.

Thirst

Rarely feeling thirsty is a good sign. Feeling thirsty all day is a sign to drink earlier.

How you feel

Headaches, tiredness and poor focus can all come from too little water.

Mistakes to avoid

These are the common ways water goes wrong.

• Following "8 glasses a day" whatever your size and day
• Forgetting to drink more on hot days or long workouts
• Drinking huge amounts at once instead of through the day
• Counting only water, when other drinks and food count too

Drink through the day, and more when you sweat.

Water and the rest of your day

Water works with the rest of your habits, not on its own.

The morning routine generator builds a glass of water into the start of your day.

Who is the water intake calculator for?

It's for anyone who trains or travels to hot places, and these tools go with it.

• Calories burned calculator – for what your workout took out of you
• TDEE calculator – for what you burn in a day
• Morning routine generator – for building water into your mornings
• Sleep calculator – for the other half of feeling good

Set your number here, then keep a bottle where you work.

More health calculators

Every health calculator reads the same "You", so you only enter yourself once.

After a long run, the running pace calculator shows your splits.