Water Intake Calculator + Printable Chart by Weight
Enter your weight and activity — get your daily target in ounces, liters, and 8-oz glasses, plus a print-ready sheet covering 100 to 250 lb. Free, no signup.
How much water you need scales with your body size and how active you are. Enter your weight and activity level for a daily target in liters, ounces, and glasses — from the mL-per-kg rule of thumb, with the U.S. Dietary Reference Intakes as the reference.
How much water do you really need?
There's no single number that fits everyone — needs scale with body weight, activity, and climate. A common rule of thumb is roughly 30–40 mL of fluid per kilogram of body weight per day, which is what this calculator uses, nudged up for higher activity.
The U.S. National Academies set total-water Adequate Intakes of about 3.7 liters per day for men and 2.7 liters for women. 'Total water' includes the water in food — usually about 20% — so the amount you actually drink is lower than those headline figures, which is what this tool estimates.
How much water should I drink a day? (chart by weight)
Find your weight, read across. Every figure is water from drinks for one day, at the three activity levels this calculator offers — 31, 35, and 40 mL per kilogram of body weight. In ounces that works out to roughly half an ounce per pound, a little more once you are active. Print the chart to keep the whole range on the fridge.
- A 135 lb woman, moderately active: 72 oz a day — 2.1 liters, about 9 glasses of 8 oz.
- A 150 lb adult, moderately active: 81 oz — 2.4 liters.
- A 200 lb adult, moderately active: 107 oz — 3.2 liters.
- That same 135 lb woman on a desk day: 64 oz. After a hard training session: 83 oz.
| Body weight | Sedentary | Moderately active | Very active |
|---|---|---|---|
| 100 lb · 45.4 kg | 48 oz · 1.4 L | 54 oz · 1.6 L | 61 oz · 1.8 L |
| 110 lb · 49.9 kg | 52 oz · 1.5 L | 59 oz · 1.7 L | 67 oz · 2.0 L |
| 120 lb · 54.4 kg | 57 oz · 1.7 L | 64 oz · 1.9 L | 74 oz · 2.2 L |
| 130 lb · 59.0 kg | 62 oz · 1.8 L | 70 oz · 2.1 L | 80 oz · 2.4 L |
| 140 lb · 63.5 kg | 67 oz · 2.0 L | 75 oz · 2.2 L | 86 oz · 2.5 L |
| 150 lb · 68.0 kg | 71 oz · 2.1 L | 81 oz · 2.4 L | 92 oz · 2.7 L |
| 160 lb · 72.6 kg | 76 oz · 2.2 L | 86 oz · 2.5 L | 98 oz · 2.9 L |
| 170 lb · 77.1 kg | 81 oz · 2.4 L | 91 oz · 2.7 L | 104 oz · 3.1 L |
| 180 lb · 81.6 kg | 86 oz · 2.5 L | 97 oz · 2.9 L | 110 oz · 3.3 L |
| 190 lb · 86.2 kg | 90 oz · 2.7 L | 102 oz · 3.0 L | 117 oz · 3.4 L |
| 200 lb · 90.7 kg | 95 oz · 2.8 L | 107 oz · 3.2 L | 123 oz · 3.6 L |
| 210 lb · 95.3 kg | 100 oz · 3.0 L | 113 oz · 3.3 L | 129 oz · 3.8 L |
| 220 lb · 99.8 kg | 105 oz · 3.1 L | 118 oz · 3.5 L | 135 oz · 4.0 L |
| 230 lb · 104.3 kg | 109 oz · 3.2 L | 123 oz · 3.7 L | 141 oz · 4.2 L |
| 240 lb · 108.9 kg | 114 oz · 3.4 L | 129 oz · 3.8 L | 147 oz · 4.4 L |
| 250 lb · 113.4 kg | 119 oz · 3.5 L | 134 oz · 4.0 L | 153 oz · 4.5 L |
Water from drinks, at 31 / 35 / 40 mL per kg of body weight — the rule of thumb this calculator runs on, not a federal target. Total water, counting the water in food, is higher; the official life-stage numbers are below.
The '8 glasses a day' myth
Eight 8-ounce glasses (about 1.9 L) is a memorable slogan, not a medical guideline — and for many people it's an underestimate once body size and activity are accounted for. A few things that actually help:
- Thirst is a reasonable guide for healthy adults
- Tea, coffee, and milk all count toward your daily total
- Pale-yellow urine is an at-a-glance sign you're well hydrated
The official targets, by life stage
The National Academies set total-water Adequate Intakes — everything you drink plus the water in food, which is about 20% of the total for most people. They're the reference this calculator compares against, and the same values our DRI calculator reports for every life stage.
| Life stage | Total water / day |
|---|---|
| Children 1–3 | 1.3 L (44 oz) |
| Children 4–8 | 1.7 L (57 oz) |
| Boys 9–13 | 2.4 L (81 oz) |
| Girls 9–13 | 2.1 L (71 oz) |
| Boys 14–18 | 3.3 L (112 oz) |
| Girls 14–18 | 2.3 L (78 oz) |
| Men 19+ | 3.7 L (125 oz) |
| Women 19+ | 2.7 L (91 oz) |
| Pregnancy | 3.0 L (101 oz) |
| Lactation | 3.8 L (128 oz) |
NASEM Dietary Reference Intakes (2005): total water, from drinks and food combined.
Formula & sources
Fluid from drinks
W = weight in kg. A rule of thumb for fluid from drinks. Total-water reference (drinks + food): the U.S. DRI sets ~3.7 L/day for men and ~2.7 L/day for women.
Sources
- Institute of Medicine (2005) Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. Washington, DC: National Academies Press — the total-water Adequate Intakes by life stage and the ~80/20 drinks-to-food split.
- Holliday MA, Segar WE (1957) The maintenance need for water in parenteral fluid therapy. Pediatrics 19(5):823–832 — the origin of weight-scaled maintenance-fluid estimation, the clinical convention behind mL-per-kg rules of thumb.
- Phillips PA, Rolls BJ, Ledingham JG, et al. (1984) Reduced thirst after water deprivation in healthy elderly men. N Engl J Med 311(12):753–759 — the age-blunted-thirst finding behind the advice that older adults drink on a schedule.
- Hew-Butler T, Rosner MH, et al. (2015) Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference. Clin J Sport Med 25(4):303–320 — overhydration risk concentrates in prolonged endurance exercise.
Water intake FAQ
How much water should I drink a day?
It depends on your size and activity, but a useful estimate is about 30–40 mL of fluid per kilogram of body weight. For reference, the U.S. DRI total-water targets are roughly 3.7 L/day for men and 2.7 L/day for women, including the water you get from food.
Does coffee or tea count toward water intake?
Yes. Despite the old belief that caffeine is dehydrating, the fluid in coffee, tea, milk, and most drinks counts toward your daily total. Water and unsweetened drinks are still the best choice for hydration without added sugar.
Should I really drink 8 glasses of water a day?
The '8 glasses' rule is a rough slogan, not an official guideline — and it's often too little once weight and activity are considered. Use your weight-based target as a starting point and adjust up in heat or with exercise.
How do I know if I'm drinking enough?
Pale-yellow urine and infrequent thirst are good everyday signs. Dark urine, headaches, or fatigue can signal you need more, especially in hot weather or during exercise.
How much water should I drink based on my weight?
Multiply your weight in kilograms by 30–40 mL — roughly half an ounce or a bit more per pound. At the moderately active 35 mL/kg this calculator uses, a 150 lb person lands near 81 oz (2.4 L) a day and a 200 lb person near 107 oz (3.2 L).
Is 64 oz of water a day enough?
64 oz (about 1.9 L) matches the weight-based target for a roughly 120 lb adult at moderate activity — enough for smaller or less active people, an underestimate for most others. The DRI total-water references are higher: about 125 oz for men and 91 oz for women, counting the ~20% that comes from food.
Is 100 oz of water a day too much?
For most healthy adults, no. 100 oz (about 3 L) of fluid is in range for larger or very active people, and healthy kidneys can process much more. True overhydration is rare and mostly a risk during prolonged endurance exercise; drinking to thirst keeps you clear of it.
Does your water intake change with age?
The adult targets are flat from age 19 on — 3.7 L total water for men, 2.7 L for women — with lower values for children and teens (see the life-stage table above). What changes is thirst: it blunts with age, so older adults often do better drinking on a schedule instead of waiting to feel thirsty.
How much water should a 135 pound woman drink?
About 72 oz a day — 2.1 liters, or roughly 9 glasses of 8 oz — at the moderately active 35 mL/kg this calculator uses. On a sedentary day it works out to 64 oz (1.9 L), and after hard training 83 oz (2.4 L). The rule scales with body weight rather than sex, so a 135 lb man works out to the same number; what moves it is activity, heat, and altitude.
Is there a chart for how much water to drink per day?
Yes — the chart above runs from 100 to 250 lb at all three activity levels, and the same rows come as a printable one-page sheet with the National Academies' total-water targets underneath. Both are computed from the formula on this page, so a printed row and the calculator always agree.
How many fl oz of water should I drink a day?
Roughly half a fluid ounce per pound of body weight, more once you are active: 81 oz at 150 lb and 107 oz at 200 lb, both at moderate activity. That is fluid from drinks. Counting the water that arrives in food as well, the National Academies' total-water references are about 125 oz a day for men and 91 oz for women.