Rex says
Same equations the textbooks use — just way less awkward. Pop in your stats and I'll tell you what the number actually means for you.
Try a scenario
Click to load — tweak from there.Inputs
Result
Ounces per day
97
Cups per day
12.1
Liters per day
2.87
Psst — share this and help Rex grow
One click, a permanent link with your numbers baked in.
How to use this
- 1Enter body weight (lb).
- 2Enter daily exercise (minutes).
- 3Read your ounces per day on the right — it updates as you type.
- 4Hit Share to keep the scenario or send it to someone.
About this calculator
A common evidence-based estimate is half your body weight in ounces as a baseline, adjusted upward for exercise since sweat losses need replacing. This calculator takes your body weight and daily exercise minutes to estimate total daily water intake in ounces, cups, and liters.
Worked example
Using the values the calculator loads with:
Inputs
- Body weight: 170 lb
- Daily exercise: 30 minutes
Results
- Ounces per day: 97
- Cups per day: 12.1
- Liters per day: 2.87
What each field means
Inputs
- Body weight (lb)
- The body weight used in the calculation, measured in lb. Starts at 170 lb so you have a working example on load. Accepted range: 50–400 lb.
- Daily exercise (minutes)
- The daily exercise used in the calculation, measured in minutes. Starts at 30 minutes so you have a working example on load. Accepted range: 0–300 minutes.
Results
- Ounces per day
- Returned as a whole number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Cups per day
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Liters per day
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How much water should I drink a day?
At 170 lb with 30 minutes of daily exercise, target about 97 ounces a day — roughly 12 cups or 2.9 liters — using the half-your-bodyweight-in-ounces baseline plus an exercise add-on.
Does the 8 glasses a day rule still apply?
8 cups (64 oz) is a reasonable floor for a smaller, sedentary adult, but it under-shoots for larger or more active people — bodyweight-based estimates scale better across individuals.
Does this include water from food and other drinks?
This estimate is total fluid intake from all sources; roughly 20% of daily water typically comes from food, so your literal drinking-water target may be somewhat lower in practice.
Do hot climates change the number?
Yes — add another 16-24 oz per day in hot or high-altitude conditions where sweat losses increase even without added exercise.
Accuracy and limitations
- Population formulas describe averages; individual bodies vary, especially at the extremes of height, age, or muscle mass.
- Results do not account for medical conditions, medication, or pregnancy.
- Use this as a directional reference, not a diagnosis — talk to a clinician before acting on it.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). How Much Water Should I Drink a Day?. Retrieved from https://www.revenuelab.fyi/toolbox/how-much-water-should-i-drink
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/how-much-water-should-i-drink" target="_blank" rel="noopener">How Much Water Should I Drink a Day? — RevenueLab</a> (2026).</p>
Source: [How Much Water Should I Drink a Day? — RevenueLab](https://www.revenuelab.fyi/toolbox/how-much-water-should-i-drink) (2026).