Daily Water Intake Calculator
How much water to drink per day from weight, exercise, and heat.
What it does
Daily water need scales with body size, then rises with sweat. A common planning rule is 35 ml per kilogram of body weight for drinks, plus roughly a glass per half hour of exercise and more in heat. Food adds about a fifth of total water on top, mostly from fruit, vegetables, and cooked grains.
The tool above applies that rule to your weight, adds for training time and hot conditions, and prints the target in liters, cups, and half liter bottles.
This is a starting target, not a prescription. Kidneys, heart conditions, pregnancy, and some medicines change fluid guidance, so anyone managing a condition should follow their clinician, not a web page.
How to use
- Enter morning body weight in your unit system.
- Pick honest daily exercise time, not the best day of the week.
- Mark hot climate when working outdoors or living through a heat wave.
- Spread the total through the day. Two big evening liters do not replace steady sipping.
Formula
- kg x 35
- Base milliliters for a normal indoor day.
- 350 per 30 min
- Training adder per half hour.
- +500 hot
- Heat and outdoor work allowance.
The 35 ml per kg base covers a typical day indoors. Each 30 minutes of moderate training adds about 350 ml, and hot conditions add another 500. Endurance sessions over 90 minutes need electrolytes too, not just water.
Worked example
Example: 70 kg, 30 minutes training, normal climate
Weight 70 kg, exercise 30 minutes, normal weather.
- Base: 70 x 35 = 2450 ml.
- Training: 30 / 30 x 350 = 350 ml.
- Total: 2450 + 350 = 2800 ml.
- Liters: 2.8 L. Cups: 2800 / 236.6 = 11.8. Bottles: 2800 / 500 = 5.6.
Reference table
| Weight | Base drinks | Cups |
|---|---|---|
| 55 kg (121 lb) | 1.93 L | 8.1 |
| 70 kg (154 lb) | 2.45 L | 10.4 |
| 85 kg (187 lb) | 2.98 L | 12.6 |
| 100 kg (220 lb) | 3.5 L | 14.8 |
Limits
- Healthy adult planning only. Conditions change guidance.
- Kidney, heart, pregnancy, and medicines need doctor limits.
- Endurance over 90 minutes needs electrolytes too.
- Altitude and illness shift need.
Common mistakes
- Counting coffee and alcohol like water. Caffeine drinks mostly hydrate, alcohol does not.
- Drinking the whole target at night and waking up hourly.
- Ignoring food water, then overshooting by a liter.
- Chasing clear urine. Pale yellow is the goal; colorless can mean overdoing it.
- Forgetting salt on long hot sessions, where water alone risks cramps.
Try it yourself
Quick checks. Answers sit tucked under each question.
85 kg, no exercise, hot climate?
85 x 35 + 500 = 3475 ml. That is 3.48 L or 14.7 cups.
Cups in 2 liters?
2000 / 236.6 = 8.5 cups.
Questions
Is 8 glasses a day right?
It fits a 60 to 70 kg adult on a quiet indoor day. Bigger bodies, training, and heat push past it.
Does coffee count?
Mostly yes for moderate amounts. Water, milk, tea, and juicy foods all add fluid; alcohol subtracts.
Can I drink too much water?
Yes, though rare in daily life. Forcing many liters in a few hours can dilute blood sodium. Drink to thirst plus the plan, not far beyond.
How do I know I drink enough?
Pale yellow urine, steady energy, and rarely feeling thirsty. Dark urine plus headaches argue for more.
Do I need more when ill?
Often, mainly with fever, vomiting, or diarrhea. Oral rehydration with electrolytes beats plain water then.