How Much Water Should I Drink Per Day Calculator
Wondering how much water you should drink per day? This free water intake calculator estimates your daily fluid target from your body weight, exercise, and climate — with results in ounces, liters, and 8-ounce glasses.
Enter your numbers
Your results
| Base intake (0.5 oz per lb) | — |
|---|---|
| Exercise adder (est.) | — |
| Climate adder (est.) | — |
| Glasses of water (8 oz) | — |
Estimate: this is a rough guideline, not medical advice. Talk to a doctor about your fluid needs if you are pregnant, older, or managing a heart, kidney, or other medical condition.
How to use this calculator
Enter your body weight and toggle between pounds and kilograms, then add the number of minutes you exercise on a typical day. Pick the climate that best matches where you live or train. Your daily water target appears instantly in ounces, liters, and 8-ounce glasses.
The exercise and climate adders are labeled as estimates — adjust your drinking up or down based on thirst, urine color, and how you feel. Use the result as a daily habit goal rather than a strict prescription.
How it works
The calculator starts with the popular half-ounce-per-pound rule: your body weight in pounds multiplied by 0.5 gives a base target in fluid ounces. A 180 lb person therefore gets 90 oz per day, which converts to about 2.7 liters. It then adds two estimated adders: about 12 ounces for every 30 minutes of exercise, and a climate adder (0 oz temperate, 16 oz hot, 12 oz humid, 28 oz hot and humid) to account for extra sweat loss.
Assumptions: the base rule is a general wellness guideline rather than a clinical standard, and the exercise and climate adders are rough estimates that vary with intensity, clothing, and individual sweat rate. The output is labeled an estimate for general health guidance only — it is not medical advice.
Frequently asked questions
How much water should I drink per day?
A widely used rule of thumb is half an ounce of water per pound of body weight each day, so a 180 lb person aims for about 90 ounces. Add roughly 12 ounces per 30 minutes of exercise and extra for hot or humid weather. It is a general guideline, not a medical prescription.
Is the 8 glasses a day rule enough?
The 8 by 8 rule (eight 8-ounce glasses, or 64 ounces) is a reasonable minimum for many smaller or less active adults, but it can fall short for larger people or anyone who exercises in heat. This calculator personalizes the target using your actual body weight, activity, and climate.
Does coffee or tea count toward my water intake?
Yes. Coffee, tea, milk, and other fluids all contribute to daily fluid intake, and moderate caffeine is only mildly diuretic. However, water is still the simplest way to hit your target, and this calculator expresses the goal in plain water servings.
Should I drink more water when I exercise?
Yes. Exercise increases fluid loss through sweat, so this calculator adds about 12 ounces per 30 minutes of activity as an estimate. Long or intense sessions in heat may require electrolytes as well as water.
Can you drink too much water?
It is possible to overhydrate, a rare but serious condition called hyponatremia, usually from drinking very large amounts in a short time. For most healthy people, following this calculator's guideline and drinking to thirst is safe.