Daily Water Intake Calculator
Enter your weight, daily exercise time and local climate. The tool starts from 35 ml per kg, adds 12 ml per minute of exercise, then applies a climate uplift — final amount is shown in litres, cups and 500 ml bottles for quick comparison.
Please enter a valid number
Recommended daily water
2.3 L
2,275 ml
Breakdown
- Base (35 ml × weight) —
- Exercise top-up (12 ml × min) —
- Climate uplift —
All beverages count (tea, coffee, soup), not just plain water. People with kidney, heart or pregnancy conditions should follow medical advice instead of this generic formula.
Formula
Water (ml) = (35 × weight_kg + 12 × exercise_min) × climate_factor Climate factor: temperate = 1.00; hot = 1.10; very hot / humid = 1.20 Floor: adult men ≥ 2,000 ml, adult women ≥ 1,600 ml (EFSA Adequate Intake × 0.8)
- · Base uses 35 ml/kg, which sits inside the clinically common 30–35 ml/kg/day range for general adult fluid needs.
- · Exercise top-up is 12 ml per minute (~360 ml per 30 min), in line with ACSM advice of 200–300 ml every 15–20 min during activity.
- · Climate uplift follows Mayo Clinic guidance to drink more fluids in hot or humid weather; Hong Kong summers often clear 30 °C, so the Hot or Very Hot options are realistic defaults.
- · "Water" here includes all beverages and food moisture — tea, coffee, soup, sports drinks, fruit, vegetables — not just plain water.
- · A floor is applied at low body weights using EFSA Adequate Intake (men 2.0 L, women 1.6 L of beverage water), so very small inputs are not under-estimated.
- · Sources: IOM 2004 / EFSA 2010 Adequate Intakes; Mayo Clinic "Water: How much should you drink every day?"; ACSM Position Stand on Exercise and Fluid Replacement.
- · People with kidney disease, heart failure, cirrhosis, pregnant women and endurance athletes should follow individualised medical/coaching advice — this generic formula does not apply.
Frequently asked
Is the "8 glasses of water a day" rule still accurate?
Eight 250 ml glasses comes out to 2,000 ml, which roughly matches the EFSA/IOM Adequate Intake for adult women (1.6–2.0 L of beverages). But that's an average — real needs vary widely by weight, exercise and climate. A 50 kg desk worker may only need ~1.8 L, while an 80 kg person training for an hour in 35 °C heat can easily exceed 4 L. This tool tailors the number to your inputs rather than giving everyone the same eight glasses.
Do coffee and tea count toward my daily water intake?
Yes. Caffeine is mildly diuretic, but at typical intake (< 400 mg/day ≈ 3–4 cups of coffee) the net hydration is still positive — a 2014 randomised crossover trial in PLOS ONE (Killer et al.) found no difference in daily fluid balance between coffee and water. Tea and soup count too. Alcohol does not (net diuretic), and try not to rely on sugary drinks (soda, juice) as your main source.
Is it possible to drink too much water?
Yes. Drinking more than ~1 L per hour for several hours can dilute blood sodium and cause hyponatraemia — there have been fatal cases in marathon and ultra-endurance events. For typical adults spreading 3–4 L across a whole day, the risk is very low. Warning signs include consistently colourless urine, frequent night-time urination, headaches, nausea or muscle cramps. People with kidney, heart or liver disease must stick to the daily fluid limits their care team sets and should not use a generic formula.
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