Water Intake Calculator
Most adults need roughly 2 to 3 litres (8 to 12 cups) of drinking water a day, plus extra on days you exercise. Enter your weight, climate and any workouts to get your rest-day and training-day numbers.
How much water should I drink a day?
- • Rest day: about 33 ml per kg of body weight (roughly 0.5 fl oz per lb), a little more in hot weather.
- • Training day: add what you sweat out, from about 6 ml per kg per hour in cool conditions up to 17 ml per kg per hour in heat.
- • Food supplies around a fifth of your total water, so these figures are for drinks only.
- • Thirst and pale-yellow urine are the everyday check. These numbers are a starting point, not a prescription.
Your daily water intake
Daily water by body weight
| Body weight | Rest day | Plus a 1-hour moderate workout |
|---|---|---|
| 120 lb (54 kg) | 1.8 L (8 cups) | 2.3 L (10 cups) |
| 150 lb (68 kg) | 2.2 L (9 cups) | 2.9 L (12 cups) |
| 180 lb (82 kg) | 2.7 L (11 cups) | 3.4 L (14 cups) |
| 210 lb (95 kg) | 3.1 L (13 cups) | 4.0 L (17 cups) |
Race day: fluid and sodium per hour
On a long race you drink to a per-hour target, not a daily one. Enter your weight, expected race time and conditions for an hourly fluid and sodium plan.
| Weather | Fluid per hour (per 70kg athlete) | Sodium target |
|---|---|---|
| Cool (<15°C) | 400–500 ml | 300–500 mg/hr |
| Moderate (15–25°C) | 600–750 ml | 500–800 mg/hr |
| Hot (25–30°C) | 800–1000 ml | 800–1200 mg/hr |
| Very hot (>30°C) | 1000–1400 ml | 1000–1500 mg/hr |
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How this calculator works
Rest-day drinking water = body weight (kg) × 33 ml × a climate factor (1.0 temperate, 1.1 hot, 1.2 very hot or humid), kept between 1.5 and 4 litres. Each workout adds body weight × a conditions-adjusted 6–17 ml per kg per hour. Race day uses the same per-hour coefficient, with sodium scaled to fluid and weather. For reference, EFSA's adequate total water intake is 2.0 L a day for women and 2.5 L for men, about a fifth of it from food.
Assumptions
- • A healthy adult with normal kidney function and typical food intake.
- • Sweat losses scale linearly with body weight within each conditions band.
- • Race-day sodium targets assume isotonic or moderately hypotonic mixes (not pure water).
Limitations
- • Humidity is only modelled through the very hot or humid climate option; altitude, illness, caffeine and alcohol are not modelled.
- • Individual sweat rates vary 2–3× in the same conditions.
Who this is for
- • Adults who want a daily drinking-water target that accounts for their size and climate.
- • Anyone who trains and wants a separate number for workout days.
- • Triathletes and endurance athletes planning race-day fluid and sodium.
Who this is not for
- • People with kidney, heart or liver conditions, or on a fluid restriction. Follow your clinician.
- • Pregnant or breastfeeding people, whose needs are higher than these figures.
- • Athletes with a measured sweat profile, who should use their own sweat rate instead.
Water intake FAQs
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