How much water should you drink a day?
You get two numbers: the official guideline for your life stage, and a personal goal that adds your size and activity. Both are water to drink, in fl oz and cups; food covers the rest.
Your water intake
Official guideline
74 fl oz
About 9 cups a day from drinks (91 fl oz counting food). National Academies.
Your personal goal
95 fl oz
About 12 cups a day
The guideline is what the National Academies set for healthy adults; it doesn't change with weight. Your personal goal starts from it and adds a little for a larger body and for regular exercise; it's the same goal the Hydrate app sets. Neither is medical advice: if you have kidney or heart conditions, or take medicines that affect fluids, ask your doctor.
How the two numbers are worked out
The National Academies' Adequate Intake, by sex and life stage, from drinks:
- Women 19+: 74 fl oz (91 counting food)
- Men 19+: 101 fl oz (125 counting food)
- Pregnant: 78 fl oz (101 counting food)
- Breastfeeding: 105 fl oz (128 counting food)
Source: National Academies of Sciences, Engineering, and Medicine, 2005. About 20% of the water people take in comes from food.
- Base: the guideline from drinks (74 fl oz for women, 101 for men), or more for larger bodies: 28 ml per kg, the common 35 ml/kg total-water estimate minus the ~20% food supplies
- + Pregnancy or breastfeeding: the National Academies' increase from drinks, +3 fl oz or +30 fl oz
- + Exercise: 0 to 25 fl oz for regular training (the guideline already covers everyday activity)
Kept between 50 and 135 fl oz a day. Hot days and big workouts add more on the day. Not the "half your body weight in ounces" rule, which is a myth we checked.
More on where these numbers come from: how much water women need, in cups and hydration statistics.
Water intake by weight
Personal goal for a woman with moderate activity. The guideline for every adult woman is 74 fl oz from drinks; larger bodies get a little more.
| Weight | Goal (fl oz) |
|---|---|
| 100 lbs | 83 oz |
| 110 lbs | 83 oz |
| 120 lbs | 83 oz |
| 130 lbs | 83 oz |
| 140 lbs | 83 oz |
| 150 lbs | 83 oz |
| 160 lbs | 83 oz |
| 170 lbs | 83 oz |
| 180 lbs | 86 oz |
| 190 lbs | 90 oz |
| 200 lbs | 94 oz |
| 220 lbs | 103 oz |
| 240 lbs | 112 oz |
Tap any weight for its own page with every activity level.
Common questions
How much water should I drink a day?
The National Academies' guideline is about 74 fl oz (9 cups) a day from drinks for adult women and about 101 fl oz (13 cups) for men, or 91 and 125 fl oz counting water from food. These are typical intakes of healthy people, not hard minimums; activity, heat and health change what you need.
Is the "half your body weight in ounces" rule accurate?
No study or health body sets water needs that way. The National Academies set intakes by age, sex and life stage, not weight. The personal goal on this page starts from that guideline and only adds a little for a larger body, so it stays close to the official figure.
Is 8 glasses of water a day accurate?
A 2002 review in the American Journal of Physiology found no scientific studies supporting the advice to drink eight 8-oz glasses of water a day. For most women the guideline works out to about 9 cups from all drinks, not 8 glasses of plain water.
Does coffee or tea count toward my water intake?
Yes. The National Academies found that caffeinated drinks contribute to daily total water intake, like other beverages.
How much more water do I need while pregnant or breastfeeding?
During pregnancy the guideline rises to about 78 fl oz a day from drinks (101 fl oz counting food). While breastfeeding it's about 105 fl oz from drinks (128 fl oz total), 37 fl oz more in total than for other adult women.
Should I drink more water in hot weather?
Yes. Very active people in hot weather often need 6 liters (about 200 fl oz) or more of total water a day, the National Academies note. Drink to thirst, add water when you sweat, and have more on hot days.
Related: water in pregnancy · water while breastfeeding · does coffee count?
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