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Free hydration calculator and water intake calculator: estimate how much fluid to aim for from body weight (30–35 mL/kg wellness range, 33 mL/kg here), activity, heat, and extra exercise. See liters, mL, US fl oz, and 8 oz glasses.
Last updated: May 25, 2026
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Adds ~350 mL per 30 minutes (rough sweat replacement hint).
Approx. total beverages + water-rich foods
3.45 L
~3446 mL · ~117 fl oz (US) · ~14.6 × 8 oz glasses
Base ~2475 mL from weight × 33 mL/kg, scaled by activity (1.18×) and climate (1×), plus ~525 mL from extra exercise time.
Not medical advice. Heart or kidney conditions, medications, and pregnancy change fluid needs—ask your clinician. Thirst, urine color, and weight change are practical checks.
75 kg · moderate activity · mild climate · 45 min extra exercise
3.45 L
3446 mL · ~117 fl oz · ~14.6 × 8 oz
2921 mL
Base 2475 mL from 75 kg
+525 mL
Sweat replacement hint only
Default (75 kg mod, 45 min)
~3.45 L · 3446 mL
70 kg · sedentary · mild
~2.31 L (2310 mL)
80 kg · active · hot · 60 min
~4.60 L (4603 mL)
160 lb · active · warm · 30 min
~3.70 L (3701 mL)
| Weight | Base (33 mL/kg) | Total (×1.18) | Liters · 8 oz cups |
|---|---|---|---|
| 60 kg | 1980 mL | 2336 mL | 2.34 L · ~9.9 cups |
| 70 kg | 2310 mL | 2726 mL | 2.73 L · ~11.5 cups |
| 80 kg | 2640 mL | 3115 mL | 3.12 L · ~13.2 cups |
| 90 kg | 2970 mL | 3505 mL | 3.50 L · ~14.8 cups |
Office, driving, low steps
Regular walking, light chores
Workouts some days, on feet often
Most days strenuous
High sweat load most days
Temperate climate, AC
Summer, humid regions
Outdoor work, heat waves
Population averages — your calculator result personalizes by weight and sweat.
Thirst
Drink when thirsty; don’t ignore thirst during heat or exercise
Urine color
Pale yellow often OK; dark amber may mean drink more (many meds/vitamins change color)
Weight change
Losing >2% body weight during a session suggests rehydrate before next hard effort
Headache / fatigue
Can signal dehydration — also sleep, food, illness; context matters
National guidance emphasizes total water from beverages and food. This tool uses a coach-friendly shortcut: scale fluids with body size, bump for workload and environment, add timed exercise. It is not a substitute for clinical fluid orders.
Base (mL) = Weight (kg) × 33Subtotal = Base × Activity × ClimateTotal ≈ Subtotal + (350 mL × exercise_minutes / 30)75.0 kg × 33 = 2475 mL × 1.18 × 1 = 2921 mL + 525 mL exercise ≈ 3446 mL
Same weight at moderate + mild without extra exercise: ~2.83 L (2826 mL).
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Suggested hashtags: #Hydration #Water #Fitness #Wellness #Calculator