# Daily Hydration Calculator

> Daily hydration calculator: find how much water you should drink a day based on your body weight and activity level. Free, runs in your browser, no signup.

- **Canonical URL:** https://boringtoolskit.com/daily-hydration-calculator/
- **Category:** Everyday Calculators
- **Evidence level:** authored-methodology
- **Reviewed:** July 26, 2026
- **Last verified:** 2026-10-12
- **Privacy:** Inputs and results stay in this browser unless the page clearly labels an external request.

## How it works

Base = 33 ml per kg of body weight, plus about 12 ml per minute of daily activity, scaled by a climate factor.

## Worked example

A 170 lb (77.1 kg) person with 30 minutes of daily activity in a temperate climate: about 98 fl oz (2.9 L), 2.54 L base plus 0.35 L for activity.

## Assumptions

- Weight converts to kilograms at 2.20462 lb/kg.
- Baseline of ~33 ml per kg reflects common hydration guidance for healthy adults.
- Activity adds about 0.35 L per 30 minutes of exercise.
- Climate factor scales total need up in heat and down in cool conditions.
- Hydration from food and other beverages counts toward total intake.
- This tool provides general estimates for planning and education only; it is not medical advice and not a substitute for a qualified healthcare professional.
- Always consult your doctor or another healthcare provider about your specific situation.

## Common questions

### Is the 8x8 '8 cups a day' rule accurate?

It is a rough starting point. A weight- and activity-based estimate is more personalized.

### Do I need more water when I exercise?

Yes. This calculator adds about 0.35 L per 30 minutes of activity and scales further in heat.

### Does food count toward my water intake?

Yes. Roughly 20% of daily intake typically comes from food, so this estimate is a fluid target, not a strict total.

### Is this medical advice?

No. It is a general planning estimate. Speak with a clinician for condition-specific guidance.

## Related tools

- /bmr-calculator/
- /bmi-calculator/
- /water-intake-tracker/

## Sources

- [Calculation methodology](/methodology/)
- [Quality evidence and verification standard](/quality-evidence/)

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