How do you calculate daily water intake by weight?

This tool uses the model from the nutrifit-widgets formula docs: 30 mL × body weight in kg, +500 mL per hour of daily activity, +500 mL in heat. 75% of the total is treated as the drinking target (the rest comes from food), shown in liters and 250 mL glasses.

How many glasses of water should I drink a day?

It depends on your weight and activity — for example, a 70 kg moderately active person lands around 7–8 glasses of 250 mL per day. Run the calculator with your own numbers; the glasses output is your drinking target after food moisture is accounted for.

Are hydration calculators accurate?

They are estimates, not measurements. This one is honest about it: the 30 mL/kg model is a heuristic and does not account for illness, medication, kidney conditions, pregnancy, or extreme sweat loss. Use EFSA reference values (2.0 L/day women, 2.5 L/day men from drinks and food) as a conservative baseline and talk to a clinician if you have a condition that affects fluid balance.

Water Intake Calculator

Q: How much water should I drink per day?

A common heuristic is 30 mL per kg of body weight per day, plus 500 mL for every hour of activity and 500 mL in hot climates — that is exactly what this calculator computes. Enter your weight, activity level, and climate above for your personal target in liters and glasses.

Q: Does exercise change how much water I need?

Yes — the model adds 500 mL for every hour of daily activity, and the per-activity guidance tells you how many of your daily glasses should go toward training. Drink most of the activity fluid during and right after the session, not all at once beforehand.

What is Water intake calculator?

Water Intake Calculator — Calculate your daily water intake from body weight, activity level, and climate. Get your target in liters and glasses, plus per-activity guidance.

Implements the water-intake model documented in the vendored nutrifit-widgets formula docs (nutrifit-health/nutrifit-widgets, MIT): 30 mL per kg of body weight, plus 500 mL for every hour of daily activity, plus 500 mL in hot climates. 75% of the total counts as the drinking target (the rest comes from food moisture) and is converted to 250 mL glasses. Activity-level presets map to daily active hours (sedentary 0 h, light 0.5 h, moderate 1 h, active 1.5 h, very active 2 h) — a conventional simplification, not part of the source formula. This is a heuristic, not medical advice: it ignores illness, medication, kidney conditions, pregnancy, and extreme sweat loss. EFSA reference values (2.0 L/day for women, 2.5 L/day for men from drinks and food) remain the conservative baseline.

Why use this water intake calculator?

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Built for water intake calculator

Calculate your daily water intake from body weight, activity level, and climate. Get your target in liters and glasses, plus per-activity guidance.

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Transparent & honest

Activity-level presets (sedentary 0 h, light 0.5 h, moderate 1 h, active 1.5 h, very active 2 h per day) are a conventional simplification, not part of the vendored formula.

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Private by design

Everything runs in your browser. Your inputs never leave your device.

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Works everywhere

Fully responsive — perfect on desktop, tablet, and mobile. No app needed.

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Regularly updated

Regularly maintained and reviewed to ensure accuracy.

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Free forever

No accounts, no limits, no watermarks. Use Water Intake Calculator as much as you need.

How to use Water Intake Calculator

1Enter your body weight and pick kg or lb in the "Weight unit" field.
2Choose your activity level — from sedentary to very active — based on a typical day.
3Optionally set the climate to hot if you live or train in high heat.
4Run the calculator to get your daily water intake in liters.
5Use the glasses count and per-activity guidance to spread your drinking target across the day.

What can you do with Water Intake Calculator?

How much water should i drink per day — Calculate your daily water intake from body weight, activity level, and climate.
Daily water intake by weight — Calculate your daily water intake from body weight, activity level, and climate.
How many glasses of water a day — Calculate your daily water intake from body weight, activity level, and climate.
Does exercise change how much water i need — Calculate your daily water intake from body weight, activity level, and climate.
Hydration calculator accuracy — Calculate your daily water intake from body weight, activity level, and climate.

Good to know

Activity-level presets (sedentary 0 h, light 0.5 h, moderate 1 h, active 1.5 h, very active 2 h per day) are a conventional simplification, not part of the vendored formula.
75% of total water is assumed to come from drinks; the rest from food moisture (per the source docs).
A glass is 250 mL; no age-related reduction is applied (per the source docs).
Heuristic model, not medical advice — see methodology for what it ignores.

How it works

Implements the water-intake model documented in the vendored nutrifit-widgets formula docs (nutrifit-health/nutrifit-widgets, MIT): 30 mL per kg of body weight, plus 500 mL for every hour of daily activity, plus 500 mL in hot climates. 75% of the total counts as the drinking target (the rest comes from food moisture) and is converted to 250 mL glasses. Activity-level presets map to daily active hours (sedentary 0 h, light 0.5 h, moderate 1 h, active 1.5 h, very active 2 h) — a conventional simplification, not part of the source formula. This is a heuristic, not medical advice: it ignores illness, medication, kidney conditions, pregnancy, and extreme sweat loss. EFSA reference values (2.0 L/day for women, 2.5 L/day for men from drinks and food) remain the conservative baseline.

Examples

70 kg, moderately active, moderate climate

Daily target: 2.6 L — about 7.8 glasses (250 mL) from drinks.

90 kg, very active, hot climate

Daily target: 4.2 L — about 12.6 glasses (250 mL) from drinks.

150 lb, lightly active, moderate climate

Daily target: 2.3 L — about 6.9 glasses (250 mL) from drinks.

People also search for these — this tool handles them all:

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