Kids Water Intake Calculator
See how much water your child needs each day, from newborns to 18-year-olds, based on the National Academies’ Adequate Intakes — with the amount from drinks shown in litres, fluid ounces and cups.
Why hydration matters for children
Water is involved in almost everything a child’s body does: keeping temperature steady during play, carrying nutrients, supporting digestion and helping the kidneys clear waste. Children lose water all day through breathing, sweat and urine, and they rely on the adults around them to make drinks available. When they are absorbed in a game, many won’t stop to drink until they are very thirsty, and babies can’t ask for a drink at all.
Good habits start early, too. The American Academy of Pediatrics (AAP) recommends water and plain milk as the main drinks for young children, calls sugary drinks harmful to a child’s health and says caffeine is best avoided. Knowing roughly how much your child needs each day makes it easier to offer the right drinks at the right times, without worrying about hitting an exact number.
How to use this calculator
Choose your child’s age: 0–6 months, 7–12 months, or any year from 1 to 18. From age 9 a sex option appears, because the National Academies set different figures for boys and girls from that age. If your child is very active or it is hot, tick Very active or hot weather to see a clearly labelled rough allowance on top of the daily amount.
For children aged 1 and older, the headline figure is the amount that should come from drinks — water, milk and other beverages — in litres, fluid ounces and cups (1 cup = 240 mL, about 8 fl oz). You will also see the total water figure, which adds the water in food. For babies, the results explain how much comes from breast milk or formula and when plain water can start.
How it's calculated
The figures are the Adequate Intakes (AIs) for water published by the Institute of Medicine of the National Academies in its Dietary Reference Intakes report on water and electrolytes. An AI is used when there isn’t enough evidence to set a precise requirement. For water, it reflects the typical (median) intakes of healthy people in U.S. national survey data, so it describes what well-hydrated children usually take in rather than a strict minimum.
For babies, the Academies worked from milk intake instead. A baby under 6 months drinks an average of about 0.78 L of breast milk a day, which is about 87% water, giving roughly 0.68 L — rounded to an AI of 0.7 L. At 7–12 months, about 0.52 L of water from 0.6 L of milk plus about 0.32 L from complementary foods and other drinks adds up to 0.84 L, rounded to 0.8 L, of which about 0.6 L is fluid.
Total water counts drinking water, other beverages and the moisture in food. For ages 1 to 18, drinks make up roughly 70–80% of the total in the AIs, and the calculator shows both figures. The unit conversions are simple: fluid ounces = litres × 1,000 ÷ 29.57, and cups = litres × 1,000 ÷ 240.
| Age group | Total water | From drinks | Drinks in fl oz (cups) |
|---|---|---|---|
| Infants 0–6 months | 0.7 L | Milk or formula only | — |
| Infants 7–12 months | 0.8 L | 0.6 L | 20 (2.5) |
| Children 1–3 years | 1.3 L | 0.9 L | 30 (3.8) |
| Children 4–8 years | 1.7 L | 1.2 L | 41 (5.0) |
| Boys 9–13 years | 2.4 L | 1.8 L | 61 (7.5) |
| Girls 9–13 years | 2.1 L | 1.6 L | 54 (6.7) |
| Boys 14–18 years | 3.3 L | 2.6 L | 88 (10.8) |
| Girls 14–18 years | 2.3 L | 1.8 L | 61 (7.5) |
Water for babies under 12 months
The AAP says infants under 6 months old should only drink breast milk or formula, and extra water is not recommended at this age; breast milk or formula already provides the water a young baby needs. At around 6 months, babies can be introduced to water, but they only need about 4–8 fl oz (½–1 cup) a day until their first birthday, because most of their fluid still comes from breast milk or formula. The CDC gives the same 4–8 oz range, and both the CDC and the AAP say babies under 12 months should not have fruit juice.
After the first birthday, the AAP suggests about 1–4 cups (8–32 fl oz) of water a day from 12 to 24 months alongside milk, and 1–5 cups (8–40 fl oz) for 2- to 5-year-olds.
Worked example
Ella is 10. Choosing 10 years and Girl gives the AI for girls aged 9–13: 2.1 L of total water a day, of which about 1.6 L should come from drinks — 54 fl oz, or 6.7 cups. The remaining 0.5 L or so comes from food such as fruit, vegetables, soups and yogurt.
Over a school day, that could be an 8 fl oz glass of milk at breakfast, a 20 fl oz water bottle during school, 10 fl oz of water after school, and 8 fl oz each of milk and water with dinner: 54 fl oz in total. If Ella has an hour of vigorous soccer practice on a warm afternoon, the AAP’s guidance for 9- to 12-year-olds of about 3–8 fl oz of water every 20 minutes adds roughly 9–24 fl oz (0.3–0.7 L) during practice. Her twin brother’s AI is higher: 2.4 L of total water, with 1.8 L (61 fl oz, or 7.5 cups) from drinks.
Limitations & tips
These are averages, not targets to force. AIs describe the typical intakes of healthy children. A child who eats plenty of fruit, vegetables and soup needs a little less from drinks, while hot weather, sport, fever, vomiting or diarrhea all push needs up.
Watch your child, not just the number. The AAP’s warning signs of dehydration include playing less than usual, urinating less often (for infants, fewer than six wet diapers a day), a parched, dry mouth, fewer tears when crying and a sunken soft spot on a baby’s head. Being very fussy or excessively sleepy, sunken eyes, cool and discolored hands and feet, or urinating only once or twice a day point to severe dehydration. Contact your pediatrician promptly if you notice any of these signs.
Choose the right drinks. Water and plain milk should make up most of what children drink. The AAP recommends no more than 4 fl oz of juice a day at ages 1–3, 4–6 fl oz at 4–6 and 8 fl oz from 7 to 18, and advises against energy drinks for children and teens. The CDC says children under 2 should avoid caffeinated drinks such as soft drinks, tea and coffee.
Medical conditions change the picture. Children with kidney or heart conditions, or those who have been told to limit or increase fluids, should follow their doctor’s advice. This calculator is general information for healthy children and is not medical advice.
Frequently asked questions
How much water should a child drink a day?
It depends on age. Under the National Academies’ Adequate Intakes, children aged 1–3 need about 0.9 L (30 fl oz) a day from drinks and 4- to 8-year-olds about 1.2 L (41 fl oz). At 9–13 it is about 1.6 L for girls and 1.8 L for boys, and at 14–18 about 1.8 L for girls and 2.6 L for boys. Food supplies the rest of their total water.
When can babies start drinking water?
At around 6 months. The American Academy of Pediatrics says babies under 6 months should only drink breast milk or formula. From about 6 months until their first birthday they need only about 4–8 fl oz (½–1 cup) of water a day, because breast milk or formula still provides most of their fluid.
Does milk count toward my child’s water intake?
Yes. The National Academies’ figure for drinks covers all beverages, including milk and drinking water, and the water in food counts toward total water. Water and plain milk are the best everyday choices; juice should be limited, and sugary and caffeinated drinks are best avoided.
How much water does a child need when playing sports?
On top of the daily amount, the AAP says children aged 9–12 generally need about 3–8 fl oz of water every 20 minutes during vigorous exercise, and teens about 34–50 fl oz per hour. Younger children should be offered water before, during and after active play and whenever they are thirsty.
How can I tell if my child is drinking enough?
A child who is playing normally and urinating regularly is usually getting enough. The AAP lists warning signs of dehydration such as playing less than usual, urinating less often (fewer than six wet diapers a day for infants), a parched, dry mouth, fewer tears when crying and a sunken soft spot in babies. Contact your pediatrician if you notice any of these.
Why do boys and girls have different water needs from age 9?
The National Academies based children’s Adequate Intakes on typical intakes in U.S. survey data. From about age 9 those intakes diverge as boys, on average, grow larger and have higher energy needs, so the AI is 2.4 L for boys versus 2.1 L for girls at 9–13, and 3.3 L versus 2.3 L at 14–18.
Sources & references
- Institute of Medicine (National Academies) — Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate, Chapter 4: Water — source of every Adequate Intake used here, the beverage amounts for each age group and the infant milk-intake derivation.
- National Academies — DRI summary table: Total Water and Macronutrients (NCBI Bookshelf) — the total water AIs by life-stage group.
- HealthyChildren.org (American Academy of Pediatrics) — Choose Water for Healthy Hydration — no extra water under 6 months, 4–8 oz from 6–12 months, exercise fluid guidance for ages 9–12 and teens, and juice limits.
- HealthyChildren.org (AAP) — Recommended Drinks for Children Age 5 & Younger — daily water amounts from 12 months to 5 years, and advice on sugary and caffeinated drinks.
- HealthyChildren.org (AAP) — Signs of Dehydration in Infants & Children — the mild, moderate and severe warning signs listed on this page.
- CDC — Foods and Drinks to Encourage (Infant and Toddler Nutrition) — water at 4 to 8 ounces a day from about 6 to 12 months.
- CDC — Foods and Drinks to Avoid or Limit — no juice before 12 months and no caffeinated drinks before age 2.
- U.S. Food and Drug Administration — Spilling the Beans: How Much Caffeine Is Too Much? — notes the AAP’s advice against energy drinks for children and teens.
Last updated: September 2026 · How we calculate
BriskToolbox provides estimates for general information only and is not medical advice. Talk to a healthcare professional about your individual health.