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Pregnancy Water Intake Calculator

Enter your weight, trimester and activity level.

How it is calculated

The estimate has three parts added together: mL = weight × 35 + 300 + activity. Weight is in kilograms, so 35 mL per kilogram sets the base amount. A fixed 300 mL is added for pregnancy. The activity bonus is 0 mL for light, 350 mL for moderate and 700 mL for intense activity; any other value counts as light. The total is shown in millilitres, in litres (divided by 1000) and in cups of 240 mL. The trimester selection does not change the number: the same 300 mL is added in all three. There is no upper limit on the result, so a high body weight can give a very large figure. It is a rough starting point, not medical advice, and doctors may advise a different amount.

Worked example

A woman in her second trimester weighs 65 kg and does moderate activity. The base is 65 × 35 = 2275 mL. Adding the 300 mL pregnancy allowance gives 2575 mL, and the 350 mL moderate-activity bonus gives 2,925 mL. In litres that is 2.93 L, and in 240 mL cups it is 2925 / 240 = 12.19 cups. Had she chosen the third trimester, the answer would stay 2,925 mL, because trimester is not part of the formula.

Try this example →

Common mistakes

  • Entering weight in pounds. The formula multiplies by 35 mL per kilogram, so 143 lb entered as 143 would give 5,305 mL (light activity) instead of 2,575 mL for the true 65 kg.
  • Expecting the trimester to change the result. It does not; picking the third trimester instead of the first gives exactly the same amount.
  • Treating the total as plain water only. The figure is a general daily fluid estimate, and drinks such as milk, soup or tea may count toward it, depending on what your midwife advises.
  • Counting cups as a different size. Here a cup is 240 mL, so a 330 mL glass is about 1.4 cups, not 1.
  • Choosing intense activity without need. It adds 700 mL regardless of how long the exercise lasts, so use it only for genuinely sustained effort.

Sources

About this calculator

Fluid needs commonly rise during pregnancy because blood volume expands by roughly 40–50%, amniotic fluid must be produced and replenished, and a higher basal metabolic rate increases water turnover through breathing, sweat, and kidney filtration. Public health bodies such as the U.S. National Academies commonly cite a total daily fluid guideline in the range of about 2.3–3 litres (from drinks and food combined) for pregnant adults; this tool starts from 35 mL per kilogram of body weight, adds a flat 300 mL for pregnancy (the same in every trimester) and an allowance for activity level, to give a general estimate in millilitres, litres, and cups.

This tool is meant as general educational information, not personalized medical advice — individual needs vary with climate, health conditions, and pregnancy complications, so any specific target should be discussed with a midwife or doctor. It's most useful as a starting reference point for expectant parents who want a rough sense of their daily hydration needs.

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  • Editorial team

    The figure is a starting target for total fluids, built from body weight plus a fixed 300 mL and an activity allowance, and it is the same in all three trimesters. Hot weather, vomiting, or a doctor's instruction to limit or raise fluids are not modelled, so follow your midwife or doctor if their advice differs. With the default values it gives 2,925 mL. How do you keep track of what you drink in a day?

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