How much water should
you drink per day?
"8 glasses a day" was never personalized advice. Your actual water goal depends on your weight, activity level, and health considerations. Calculate yours below.
Your hydration calculator
Your daily goal
95 fl oz
That's about 11.9 cups or 2.8L per day
Track this goal automatically with AI coaching in the app.
Get Thirsty Girls — freeHow your goal is calculated
35ml × body weight (kg)
Your weight-based starting point
0–1,200ml depending on intensity
Sedentary adds 0; athlete adds 1,200ml
Pregnant +300ml · Breastfeeding +500ml
Based on clinical guidelines
Results are clamped between 50 fl oz (1,500ml) and 135 fl oz (4,000ml) per day. HealthKit integration in the app can further adjust your goal based on active calories burned.
Water intake by weight
Moderate activity level · no health considerations
| Weight | Daily goal (fl oz) |
|---|---|
| 100 lbs | 71 oz |
| 110 lbs | 76 oz |
| 120 lbs | 81 oz |
| 130 lbs | 87 oz |
| 140 lbs | 92 oz |
| 150 lbs | 97 oz |
| 160 lbs | 103 oz |
| 170 lbs | 108 oz |
| 180 lbs | 114 oz |
| 190 lbs | 119 oz |
| 200 lbs | 124 oz |
| 220 lbs | 135 oz |
| 240 lbs | 135 oz |
For your personalized calculation including activity level and health considerations, use the calculator above or browse all weight pages.
Common questions
Is "8 glasses a day" accurate?
8×8 (eight 8-oz glasses) is a commonly cited figure but it's not based on personalized science. A 120 lb sedentary person and a 200 lb athlete have very different needs. The formula used here — 35ml per kg of body weight, adjusted for activity — is grounded in exercise physiology research.
Does coffee count toward my daily water intake?
Moderate coffee consumption (1–2 cups) has minimal net dehydrating effect in habitual drinkers. However, for the purpose of building a hydration habit, tracking plain water gives you a more accurate baseline. Coffee is a bonus, not a substitute.
Should I drink more water in hot weather?
Yes — heat and humidity increase water loss through sweat. Add approximately 8–16 fl oz per day in hot conditions, or more if you're exercising in heat. The Thirsty Girls app can adjust your goal based on HealthKit active calorie data.
What if I can't hit my full goal at first?
Start with a goal you can realistically hit and build up. Increasing by 8–16 oz per week is more sustainable than jumping to your full calculated goal immediately. Consistency matters more than perfection.
How is the Thirsty Girls calculation different from other apps?
Most apps use a fixed formula without activity or health adjustments. Thirsty Girls factors in weight, activity level (5 tiers), pregnancy, and breastfeeding — and adjusts further via HealthKit for active calories burned on specific days.
Track your goal automatically
Thirsty Girls calculates your goal on day one and tracks every drop — with AI coaching that keeps you accountable.
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