How-to
How to Calculate Water Intake by Weight
Quick answer
To calculate water intake by weight, 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.
Fine-tune
Your daily goal: 2.8 litres, 11 glasses.
Your daily goal
of water a day · about 11 glasses or 5.5 half-litre bottles
- 2.8
- Litres
- 94
- Ounces
- 11
- Glasses
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 up2 glasses
- 9:00 PM · Wind down2 glasses
Ease off after 9:00 PM for better sleep.
Electrolytes? Skip them today
For everyday hydration, plain water and a normal diet cover your electrolytes just fine.
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.
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.
- 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.
- 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.