WaterDailyGoal

Step-by-step method

How to Calculate Water Intake by Weight

Quick answer

This is the step-by-step method page. To calculate water intake by weight, choose a unit, use 30–40 ml per kg or 0.5–0.75 oz per pound per day. Then adjust for activity, hot weather, pregnancy, breastfeeding, GLP-1 medication, or heavy sweating. The calculator below applies those adjustments automatically.

Quick startPick a day type
Used for the base estimate
Activity level
ClimateWhere you spend your day
Fine-tuneMeasure in bottles · Your day
Life stageOptional
Measure in bottlesOptional
Optional — see what's left
glasses
Your dayShapes the sip schedule

Saved profile

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Your daily goal: 2.8 litres, 11 glasses.

Your daily goal

Updates instantly
2.8litres

of water a day · about 11 glasses · 5.5 half-litre bottles

Planning scenarios: 2.6-3.3 litres. Use it as a flexible target, not a medical limit.

Start

2 glasses

7:00 AM

Taper

9:00 PM

for better sleep.

Food fluid

+0.7 L

typical food water

2.8
Litres
95
Ounces
11
Glasses
Why this number

WaterDailyGoal uses 33 ml/kg for a beverage planning estimate. The 30–40 ml/kg scenarios and activity/climate coefficients are site assumptions, not validated personal requirements or NAM/EFSA formulas. Pregnancy, breastfeeding, and GLP-1 medicines do not automatically change this estimate. Population total-water references include food; they are not minimum drinking doses. Follow individual clinical advice.

Full methodology

Next step

Your sip schedule

  • 7:00 AM · Start the day2 glasses
  • 9:48 AM · Top up2 glasses
  • 12:36 PM · Top up2 glasses
  • 3:24 PM · Top up2 glasses
  • 6:12 PM · Top up1.5 glasses
  • 9:00 PM · Wind down1.7 glasses

Ease off after 9:00 PM for better sleep.

Electrolytes? Not automatic

Electrolytes are not automatic. Long or heavy sweating and vomiting or diarrhea need different approaches; food, losses and medical restrictions matter. Ask a clinician or pharmacist when illness is involved.

A friendly estimate for healthy adults, not medical advice. Your needs rise with heat, exercise, illness, pregnancy, and some medications. Don't drink more than ~1 litre per hour.

Daily goal

2.8 litres

The link and preview image include your weight and settings.

Maintained by the WaterDailyGoal TeamLast updated Editorial update; not a medical review.

Worked examples

These are not new rules; they show the same formula translated into litres, ounces, glasses, and bottles.

Worked examples using the calculator baseline and moderate day defaults
PersonBaseline ruleCalculator outputEveryday translation
60 kg adult1.8–2.4 L by 30–40 ml/kg2.3 L · 78 oz9 glasses or 4.5 half-litre bottles
75 kg adult2.3–3.0 L by 30–40 ml/kg2.8 L · 95 oz11 glasses or 5.5 half-litre bottles
90 kg adult2.7–3.6 L by 30–40 ml/kg3.6 L · 122 oz14.5 glasses or 7 half-litre bottles

Example calculation

For a 75 kg adult, 75 × 33 ml = 2,475 ml, or about 2.5 litres before activity and heat adjustments. If that person trains hard or spends the day in hot weather, the target moves higher.

Why not one universal number?

The old one-size-fits-all rules are memorable, but bodies are not the same size and days are not the same. Weight gives the baseline; context finishes the estimate.

Frequently asked

What is the easiest way to calculate water intake by weight?

Use 30–40 ml per kg of body weight, or 0.5–0.75 oz per pound. Then adjust upward for activity, heat, pregnancy, breastfeeding, GLP-1 medication, or heavy sweat losses.

Should I use pounds or kilograms?

Either works. The kg formula is 30–40 ml/kg; the pound formula is 0.5–0.75 oz/lb. They produce similar ranges when converted correctly.

Why does the calculator add activity separately?

Body weight gives a baseline. Activity and heat change sweat losses, so the calculator adds a practical activity amount and climate multiplier instead of hiding everything inside one rule.

Sources

  • 1.U.S. National Academies (IOM/NAM), 2005 — Adequate total water intake of about 3.7 L/day for men and 2.7 L/day for women, including water from food and all beverages.Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate, Summary: water adequate intakes; drinks and food
  • 2.European Food Safety Authority (EFSA), 2010 — Adequate total water intake of 2.5 L/day for men and 2.0 L/day for women under temperate conditions.Scientific Opinion on Dietary Reference Values for water, EFSA Journal 8(3):1459, abstract and conclusions
  • 3.Mayo Clinic — General guidance of roughly 2.7–3.7 L of total fluids a day, with thirst and pale-yellow urine as everyday checks.