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Water Intake Calculator

Estimates daily drinking-water needs from body weight (35 ml per kg) plus an allowance for exercise time, reported in litres, millilitres and 240 ml cups.

When to use

You want a practical daily fluid target for a healthy adult based on weight and activity.

Do not use when: The person has kidney, heart or liver disease, is pregnant, or works in extreme heat; medical advice supersedes this rule of thumb.

Formula

water_ml = 35 × weight_kg + 355 × (exercise_minutes / 30)

The 30–35 ml/kg rule is a common dietetic heuristic. EFSA's adequate intake for total water (including food) is about 2.5 L/day for men and 2.0 L/day for women; roughly 20–30% of that comes from food.

Inputs

Parameter	Type	Unit	Required	Description
`weight_kg`	number	kg	yes	Body weight in kilograms. Range: > 0, ≤ 700
`exercise_minutes_per_day`	number	min	default 0	Minutes of moderate exercise per day; adds about 355 ml (12 US fl oz) per 30 minutes. Range: ≥ 0, ≤ 600

Outputs

Output	Type	Unit	Description
`water_liters_per_day`	number	L/day	Suggested drinking water per day.
`water_ml_per_day`	number	ml/day	Same amount in millilitres.
`cups_per_day`	number	cups	Number of 240 ml (8 US fl oz) cups.

Example

70 kg, 30 min exercise: {"weight_kg":70,"exercise_minutes_per_day":30} → {"water_liters_per_day":2.81,"water_ml_per_day":2805,"cups_per_day":11.7}

55 kg, no exercise: {"weight_kg":55} → {"water_liters_per_day":1.93}

GET https://tttkmbb.com/api/v1/calculate/water-intake?weight_kg=70&exercise_minutes_per_day=30

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/water-intake (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/water-intake · Markdown: https://tttkmbb.com/health/water-intake.md · JSON definition: https://tttkmbb.com/health/water-intake.json
MCP: server https://tttkmbb.com/mcp, tool run_calculator with calculator_id="water-intake"
OpenAPI operationId: calculate_daily_water_intake
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

EFSA (2010) Scientific Opinion on Dietary Reference Values for water (standard)
Mayo Clinic – Water: How much should you drink every day? (reference)

FAQ

Does coffee or tea count?

Yes, all beverages contribute to total water intake; caffeinated drinks in normal amounts are not net dehydrating.

Can I drink too much?

Yes. Drinking many litres in a short time can cause hyponatraemia. Spread intake over the day and drink to thirst during long exercise.

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TDEE Calculator — Estimate calorie needs alongside hydration.