How much water should I drink a day based on my weight?

A common practical formula is half your body weight in ounces, which works out to about 0.5 to 1 oz of water per pound (ounces per pound). For a 200 pound person that is roughly 100 oz, or close to 3 liters (3,000 mL). The National Academies of Sciences (NAS) frames the same idea as adequate intake: about 125 oz (3.7 L, 15.5 cups) per day for an adult man and 91 oz (2.7 L, 11.5 cups) per day for a woman, including water from food. The calculator starts from your weight and then adjusts for activity level, climate, caffeine, alcohol, pregnancy, and your goal.

Is the half body weight in ounces rule right?

It is a reasonable starting point, not a hard rule. Half body weight in ounces (the 0.5 to 1 oz per lb range) lands close to the NAS adequate intake for most adults, and it is easier to remember than 8 cups (64 oz) or a gallon (128 oz). It can under-shoot for very active people in hot weather and over-shoot for small, sedentary people, which is why this calculator layers activity, climate, and goal adjustments on top of the baseline rather than stopping at body weight alone.

Does coffee count as water?

Yes, mostly. Killer et al. 2014 (PLOS ONE) found that moderate coffee intake (up to 4 cups per day) provides hydration similar to plain water in habitual coffee drinkers. The diuretic effect of caffeine is mild and offset by the fluid in the drink itself. The calculator adds a small offset (about +10 oz per 200 mg caffeine) to account for the diuretic effect at higher doses.

Can I drink too much water?

Yes. Hyponatremia (water intoxication) happens when blood sodium drops too low from drinking too much water too fast. It is rare but documented in endurance athletes and people on strict water diets. Noakes 2003 (BJSM) describes cases of exercise-associated hyponatremia at intakes above 6 L (200 oz) per day. The calculator flags any target above 200 oz.

How much water should a woman drink a day, and a man?

The NAS adequate intake is about 91 oz (2.7 L, 11.5 cups) per day for an adult woman and 125 oz (3.7 L, 15.5 cups) per day for an adult man, both including water from food. Women sit lower mainly because they average lower body weight, lower lean body mass, and lower total body water (about 52% of body weight vs 60% for men). The calculator applies a small downward adjustment for female biology and an upward one for male biology when weight is provided.

How much water should I drink if I exercise 30 minutes, or in hot weather?

Add roughly 12 to 16 oz (350 to 470 mL) of water for every 30 minutes of exercise on top of your baseline, and more in hot weather. ACSM recommends 17 to 20 oz (500 to 600 mL) about 2 to 3 hours before exercise, 8 oz (240 mL) during warm-up, and 7 to 10 oz (200 to 300 mL) every 10 to 20 minutes during the session, then replacing 16 to 24 oz per pound of body weight lost in sweat. A higher sweat rate or hot, humid climate raises the loss, so the calculator adds water for both your activity level and climate, and reminds you to replace electrolytes (sodium and potassium) for long sessions.

How do I know if I am hydrated?

Urine color is the most practical at-home check: pale straw or light yellow means good hydration, dark yellow to amber means dehydration, and persistently clear urine can mean over-hydration. The chart on this page uses the same color codes the Cleveland Clinic and Mayo Clinic publish. If you hit your target and still feel thirsty all the time, the cause can be high salt or caffeine intake, hot weather, exercise, dry indoor air (winter heating, AC), or medications such as diuretics, lithium, or some blood-pressure drugs. Constant thirst can also signal diabetes or thyroid issues, so see your doctor if it persists.

What counts toward my daily water target?

Water from food and other drinks counts, not just plain water. About 20% of total fluid intake comes from food in a typical US diet: watermelon is 92% water, cucumber 95%, lettuce 96%, strawberries 91%, oranges 87%, and soup is 85 to 95%. Plain unsweetened sparkling water hydrates the same as still water because carbonation does not affect fluid absorption, though you should watch for added sugar in flavored versions. The calculator already accounts for food in the NAS-based baseline, since the 91 oz / 125 oz numbers include it.

How much water during pregnancy?

The Institute of Medicine recommends 101 oz (3.0 L) per day during pregnancy and 128 oz (3.8 L) per day while breastfeeding. The calculator adds 10 oz for pregnancy and 32 oz for breastfeeding to your personalized base.

How much water should I drink to lose weight?

Drink 16 to 20 oz (500 to 600 mL) about 30 minutes before each major meal. Dennis et al. 2010 (Obesity) showed adults who drank 500 mL before meals lost 44% more weight over 12 weeks than those who did not. Water blunts appetite hormones and adds zero calories, and unsweetened sparkling water can feel more filling. The Weight loss goal in the calculator adds 16 oz to your baseline target.

Does drinking water clear skin?

Mild dehydration tightens skin and accentuates fine lines, so reaching your daily target supports skin elasticity. The 'drink water to fix acne' claim is overstated: there is no strong randomized evidence that hydration alone clears acne. Use the Skin health goal for an extra 8 oz baseline.

How much water for a hangover?

Alcohol is a strong diuretic: about 4 oz of fluid is lost per standard drink. For a hangover, replace 16 to 24 oz of water plus electrolytes (sodium and potassium) over the first 2 to 3 hours. The Alcoholic drinks field in the calculator adds 6 oz per drink to your daily target to compensate.

Is 8 glasses a day actually correct, and what about a gallon?

Eight 8 oz glasses (64 oz total) is a useful rule of thumb but is not a personalized target, and a full gallon (128 oz) is more than most people need. The NAS and IOM publish higher numbers than 8 cups: 91 oz (2.7 L) for women and 125 oz (3.7 L) for men including food. The calculator gives a personalized target in ounces, milliliters, liters, and cups that beats the generic 8-glass rule for almost everyone.

How much water should you drink today?

Calculate my target

Most adults need about half an ounce to one ounce of water per pound of body weight each day, roughly 11.5 cups (2.7 liters) for women and 15.5 cups (3.7 liters) for men as a baseline. Add 12 to 16 oz for every 30 minutes of exercise, and more in hot weather. Enter your weight and activity below for your exact target in oz, mL, liters, and cups.

Based on NAS & IOM dataLive progress trackerDiuretic-aware (caffeine + alcohol)

Units

Weight (lbs)

Base target = body weight / 2 in oz.

Age

65+ adds 8 oz for reduced thirst.

Gender

Wake time

Bedtime

Activity & climate

Sweat losses add ounces to your daily target.

Activity level

Moderate exercise 3 to 5 days a week

Climate

60 to 80 F (15 to 27 C)

Quick preset

Sweat math: Endurance athletes lose 0.5 to 2 L per hour in heat (ACSM). Replace with 16 to 24 oz per pound of body weight lost.

Diuretic intake

Caffeine and alcohol increase fluid loss.

Caffeine (mg per day)

+10 oz water per 200 mg caffeine.

Track your caffeine here

Alcohol (drinks per day)

drinks

+6 oz water per standard drink.

Note: Coffee and tea still count as fluid (Killer 2014). Alcohol is a net loss, so we add water on top instead of counting it.

Goal

Tunes your target for a specific outcome.

Daily targetBelow 25% of target

Daily water target

128

= 3.8 L · 3,785 mL · 16.0 cups

Consumed

0 oz

0.00 L

0% of target

Remaining

128 oz

3.79 L

16 more 8 oz glasses

Progress0%

Next glass in

00:58:30

at 6:16 PM · about 11.6 oz (0.34 L)

Counter pauses automatically when this tab is hidden.

Log a glass

Bottle equivalents

Your 128 oz (3.79 L) target equals:

Standard 8 oz (0.24 L) glasses16.0
16 oz (0.47 L) reusable bottles8.0
Hydro Flask 24 oz (0.71 L)5.3
Nalgene 32 oz (0.95 L)4.0

Hourly schedule

11 glasses

From 7:00 AM to 10:30 PM.

7:00 AM
11.6 oz0.34 L
8:25 AM
11.6 oz0.34 L
9:49 AM
11.6 oz0.34 L
11:14 AM
11.6 oz0.34 L
12:38 PM
11.6 oz0.34 L
2:03 PM
11.6 oz0.34 L
3:27 PM
11.6 oz0.34 L
4:52 PM
11.6 oz0.34 L
6:16 PM
11.6 oz0.34 L
7:41 PM
11.6 oz0.34 L
9:05 PM
11.6 oz0.34 L

Electrolyte drinks compared

Heavy training in heat needs more than water. See LMNT vs Liquid IV vs DIY mixes.

Open guide

Saved locally

Daily log history

Up to 8 days stored in this browser only. Use it to spot trends.

Save your first daily log to see it here

Log at least one glass and click Save daily log.

Method

Three steps to your hydration plan.

Enter your body data, pick your activity level and climate, then track glasses as you drink them. Your target shows in ounces, milliliters, liters, and cups.

Step

Enter your body data

Weight, age, gender. Toggle pregnancy or breastfeeding if either applies. The base target is body weight in pounds divided by 2 in ounces.

base = lbs / 2 oz

Step

Pick activity, climate, diuretics

Activity and climate add ounces for sweat losses. Caffeine and alcohol add ounces to compensate for their diuretic effects. Pick your goal (general, athletic, skin, energy, or water to lose weight, which adds a pre-meal pour).

target = base + activity + climate + diuretics + goal

Step

Track glasses live

Tap 8 oz, 16 oz, 24 oz, or custom buttons through the day. The progress bar fills and the next-glass countdown updates every second. Save daily logs for trend tracking.

progress = consumed / target

Back to calculator

The science

How we get to your number.

Four mechanisms drive daily water need. Each is anchored in NAS, IOM, ACSM, or peer-reviewed clinical research.

Base formula

Body weight / 2 in oz

The most-cited practical formula in US clinical practice, roughly 0.5 to 1 oz of water per pound (ounces per pound) of body weight. A 150 lb adult lands at 75 oz of plain water before adjustments. The NAS Adequate Intake of 91 oz (women) and 125 oz (men) includes water from food and matches this base for typical body weights.

Marker

base_oz = weight_lb / 2

150 lb → 75 oz baseline before activity and climate

Activity bonus

Sweat replacement

ACSM recommends 16 to 24 oz of water per pound of body weight lost in sweat, and roughly 12 to 16 oz extra for every 30 minutes of exercise. We translate activity tiers into a fixed ounce add-on: +12 (light), +20 (moderate), +32 (very active), +48 (athlete). A higher sweat rate means a bigger add-on, and athletes in heat may need to add electrolytes.

Marker

activity_bonus = {0, 12, 20, 32, 48}

Moderate exerciser at 150 lb → 75 + 20 = 95 oz

Climate bonus

Heat stress

In hot weather or humid environments, fluid loss can reach 1 to 2 L per hour during exercise, so you need more water in the heat. We add +16 oz for 80 to 95 F and +24 oz for above 95 F. Indoor AC can mask heat losses but does not eliminate them in active people.

Marker

climate_bonus = {0, 0, 16, 24}

Outdoor worker at 95 F → +24 oz on top of base

Diuretic offset

Caffeine and alcohol

Killer et al. 2014 (PLOS ONE) showed coffee is mostly hydrating, but at higher caffeine doses the diuretic effect creates a small fluid debt. Alcohol has a stronger diuretic effect (~4 oz per drink). We add +10 oz per 200 mg caffeine and +6 oz per standard drink.

Marker

diuretic_offset = caffeine/200 × 10 + alcohol × 6

2 lattes + 1 beer → +15 oz on top of base

Hydration check

Read your urine color.

The fastest at-home hydration test. Pale straw is the goal, dark amber is dehydrated. Same color codes the Cleveland Clinic and Mayo Clinic publish in patient handouts.

Clear / pale

Overhydrated

Constantly clear urine for hours may signal you are drinking past your needs. Cut back if persistent.

Pale straw

Well hydrated

The ideal color: pale, light yellow. Indicates good hydration without being excessive.

Yellow

OK, drink soon

Standard daytime urine. You are not dehydrated yet, but the next glass of water should be soon.

Dark yellow

Mildly dehydrated

Drink 16 oz now. Mild dehydration can already affect focus, headache, and mood (Ganio 2011).

Amber / brown

Dehydrated

Drink 24 oz now and rest. If urine is still amber after rehydrating, or has blood, see a clinician.

The concept

What is water turnover?

Water turnover is the total volume of water moving through your body each day, in and out. It is the reason a single flat recommendation cannot work for everyone: two people the same weight can turn over very different amounts depending on how much they sweat, how hot it is where they live, and how much water their food carries.

Water in

Where it comes from

Beverages: water, coffee, tea, milk, and juice. Roughly 80% of total intake.
Food: about 20% of intake, mostly from fruit and vegetables.
Metabolic water: a small amount produced when your body burns carbohydrate, fat, and protein.

Water out

Where it goes

Urine: the largest and most adjustable loss.
Sweat: the most variable, and the reason exercise and heat raise your target.
Breathing: water vapor leaves with every exhale, more at altitude and in dry air.
Digestion: a steady, smaller loss through the gut.

Turnover rises with body size, activity, heat, altitude, pregnancy, and fever, and falls with age as kidney concentrating ability declines. That is exactly the set of inputs the calculator above adjusts for, which is why a personalized number beats a flat rule.

Reference

Daily targets by demographic.

Adequate Intake (AI) values from the National Academies of Sciences (NAS) and Institute of Medicine (IOM). Totals include water from food and beverages. These targets sit higher than the old 8 cups (64 oz) rule yet below a full gallon (128 oz): about 2.7 liters for women and 3.7 liters for men. A weight-based shortcut, half body weight in ounces, lands a 200 pound person near 100 oz, close to the same range.

Group	oz / day	Liters	Cups (8 oz)	Source
Adult women (19+)	91	2.7 L	11.4	NAS
Adult men (19+)	125	3.7 L	15.6	NAS
Pregnant women	101	3.0 L	12.6	IOM
Breastfeeding women	128	3.8 L	16.0	IOM
Adolescents 14 to 18 (M)	112	3.3 L	14.0	NAS
Adolescents 14 to 18 (F)	78	2.3 L	9.8	NAS
Children 9 to 13	67	2.0 L	8.4	NAS
Children 4 to 8	40	1.2 L	5.0	NAS
Adults 65+ (age-adjusted)	105	3.1 L	13.1	NAS

Totals include water from food (about 20% of intake) and all beverages. NAS / IOM Dietary Reference Intakes, 2004.

What counts

Water sources, ranked.

Plain water is not your only option. Here is what fluids actually count toward your target, and how much.

100%

Plain water

Tap, filtered, or bottled. Sparkling water counts the same as still.

95%

Coffee & tea

Killer 2014 (PLOS ONE): up to 4 cups a day hydrates like plain water in habitual drinkers.

90%

Soft drinks

Counts as fluid, but adds 30 to 50 g of sugar per 16 oz. Pick diet or zero-sugar for hydration.

80%

Fruits & vegetables

Watermelon 92%, cucumber 95%, lettuce 96%, oranges 87%. About 20% of US fluid intake.

85 to 95%

Soup & broth

Broth-based soups are mostly water plus sodium. Useful when you are sick or post-exercise.

88%

Milk & dairy

Plus 8 g protein and electrolytes per cup. James 2019 found milk among the most hydrating drinks.

95%

Sports drinks

95% water plus sodium and potassium. Useful only for sessions over 60 minutes or in heat.

Net loss

Alcohol

Strong diuretic. About 4 oz of fluid lost per standard drink. Do NOT count toward your target.

100%

Sparkling water

Same hydration as still water. Carbonation does not affect fluid absorption. Pick unsweetened.

In practice

How to actually hit your target.

Knowing your number is the easy part. Most people fall short because hydration is a habit problem, not a math problem. These are the changes that move the needle.

Build the habit

Make water the default

Keep a marked bottle within arm's reach while you work, so drinking never requires a decision.
Drink on a schedule rather than waiting for thirst, which lags actual need and blunts further with age.
Anchor a glass to something you already do every day: before each meal, after every bathroom trip, on waking.
Swap one sugary drink a day for water. Easier to sustain than a full overhaul.
If plain water bores you, add lemon, cucumber, mint, or berries. Flavor costs nothing in hydration terms.

Cover the gaps

Where people fall short

Eat water-rich foods. Cucumber is 95% water, lettuce 96%, watermelon 92%, oranges 87%.
Replace what you sweat out. Add 12 to 16 oz for every 30 minutes of exercise, more in heat.
Drink more in hot or dry weather and at altitude, where losses through skin and breath climb quietly.
Go easy on alcohol, which suppresses vasopressin and increases urine output.
Check urine color against the chart above. It is the fastest real-world feedback you have.

Support

Frequently asked questions.

Plain-English answers about daily water targets, urine color, coffee hydration, pregnancy, and weight loss.

Still have a question?

Tell us what we missed and we will add it here.

Still have a question?

Tell us what we missed and we will add it here.

Sources & reading

Where the numbers come from.

Methodology

Data sources

Base targets come from the NAS and IOM Dietary Reference Intakes. Activity and climate adjustments come from ACSM and EFSA hydration guidelines. Coffee and tea hydration math comes from Killer 2014. Hyponatremia risk math comes from Noakes 2003.

01
National Academies of Sciences (NAS / IOM)
Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate (2004)
02
American College of Sports Medicine (ACSM)
Exercise and Fluid Replacement Position Stand (2007)
03
European Food Safety Authority (EFSA)
Scientific Opinion on Dietary Reference Values for Water (2010)
04
Killer, Blannin & Jeukendrup, PLOS ONE (2014)
No evidence of dehydration with moderate daily coffee intake
05
Noakes, BJSM (2003)
Overconsumption of fluids by athletes and exercise-associated hyponatremia
06
Dennis et al., Obesity (2010)
Water consumption increases weight loss during a hypocaloric diet intervention

Related guides

Hands-on guides on electrolytes, caffeine, low-calorie drink swaps, and dairy alternatives.

Editorial

Built by Hunzala Ashfaq, Founder

Updated May 18, 2026Cross-checked against NAS, IOM, ACSM, EFSA, and peer-reviewed hydration research

Data Sources

Daily water target uses a body-weight baseline (lb / 2 in ounces, capped at 350 lb) with adjustments for gender (NAS ±8 oz), age 65+ (+8 oz), pregnancy (+10 oz), breastfeeding (+32 oz), activity (0 to 48 oz), climate (0 to 24 oz), and diuretic intake (+10 oz per 200 mg caffeine, +6 oz per alcoholic drink). Capped above 200 oz with a hyponatremia warning. Results are educational, not medical advice.

NAS Dietary Reference Intakes for Water (IOM, 2005) — Institute of Medicine adequate intakes (91 oz/day for women, 125 oz/day for men) and pregnancy/lactation adjustments.
ACSM Position Stand: Exercise and Fluid Replacement — American College of Sports Medicine guidance on hydration before, during, and after exercise.
Killer SC et al., 2014 (PLOS ONE) — Evidence that moderate coffee intake hydrates like water in habitual drinkers.
Noakes TD, 2003 (BJSM) — Hyponatremia (water intoxication) risk thresholds for endurance athletes.
EFSA Scientific Opinion on Dietary Reference Values for Water — European reference values used for the metric (L) targets.

Related Guides

Built and maintained by Hunzala Ashfaq, founder of DrinkDigits. Last updated 2026-05-19. Calculations verified against official brand and public nutrition data.

This calculator is educational and for general reference only. It is not medical or dietetic advice. Consult a licensed healthcare provider for personalized nutrition guidance.

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How much water should you drink today?

Personal info

Activity & climate

Diuretic intake

Goal

Next glass in

Log a glass

Bottle equivalents

Hourly schedule

Electrolyte drinks compared

Daily log history

Three steps to your hydration plan.

Enter your body data

Pick activity, climate, diuretics

Track glasses live

How we get to your number.

Body weight / 2 in oz

Sweat replacement

Heat stress

Caffeine and alcohol

Read your urine color.

What is water turnover?

Where it comes from

Where it goes

Daily targets by demographic.

Water sources, ranked.

How to actually hit your target.

Make water the default

Where people fall short

Frequently asked questions.

Where the numbers come from.

Data sources

Related guides

Data Sources

Related Guides

Other free tools.

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