Water Intake Calculator
Daily water target from weight, sex, exercise, and pregnancy or breastfeeding status.
Written by Golam Rabbani, Founder & Lead Engineer — Last updated 2026-05-01
How to use this water intake calculator
- Pick kg or lb and enter your body weight.
- Select your sex so the calculator applies the right sex-based intake floor.
- Choose how much exercise you do on a typical day.
- If applicable, indicate whether you are pregnant or breastfeeding.
- Click Calculate to see daily water intake in litres, fluid ounces, and 250 ml glasses, then Copy or Reset.
About this water intake calculator
The Water Intake Calculator estimates daily drinking-water needs using a 30 ml-per-kg baseline (Mifflin-St Jeor-style hydration tables) with an adequate-intake floor of 2,200 ml for adult women and 3,000 ml for adult men, sourced from the U.S. Institute of Medicine reference values. Exercise adds about 350 ml per 30 minutes of activity, pregnancy adds 300 ml, and breastfeeding adds 700 ml — matching IOM adjustments. For example, a 65 kg pregnant woman doing 30 minutes of light cardio would compute 65 × 30 = 1,950 ml, raised to the 2,200 ml female floor, plus 350 ml exercise and 300 ml pregnancy, for a total of 2,850 ml per day. Food typically supplies an additional 20% of total water, so this drinking-water number does not need to be hit by plain water alone. This tool is for general education and is not medical advice — consult a qualified healthcare professional before changing fluid intake, especially during pregnancy, lactation, or with kidney or heart conditions.
FAQ
- Is "8 glasses a day" actually accurate?
- It is a rough average. The IOM adequate intake recommendations work out to roughly 9 glasses (250 ml) for women and 13 for men of average weight — closer than the old guideline but still highly individual.
- How does pregnancy or breastfeeding change my needs?
- IOM adds about 300 ml/day during pregnancy and about 700 ml/day during breastfeeding to support amniotic fluid, blood volume, and milk production. The calculator applies these add-ons automatically.
- Should I count tea, coffee, milk, or fruit?
- Yes. Almost all fluids count toward total water intake. The drinking-water target shown here is the portion you should aim to drink as water or unsweetened beverages — the rest comes from food and other drinks.
- What about hot weather or sauna sessions?
- Heat exposure can add 0.5–1 L per hour of sweat losses. For heavy heat days, add roughly 500 ml per hour spent sweating to the number this tool gives.
- Is there a maximum safe intake?
- Healthy kidneys excrete about 0.8–1.0 L per hour. Drinking dramatically more than this — particularly during long endurance events — can cause hyponatremia (low blood sodium). Stick to thirst plus planned exercise add-ons.