How much water should I drink a day

There's no single magic number — water needs vary with weight, climate, activity and diet. But you can reach a practical, personalized target.

The body-weight rule

A simple, widely used reference is 35 ml per kilogram (roughly half an ounce per pound) per day:

• 70 kg (154 lb) → ~2.4 L
• 90 kg (198 lb) → ~3.2 L

That's what our calculator uses, rising to 40–45 ml/kg with more intense activity.

The 8-glasses myth

"8 glasses a day" is just an approximation (8 × 8 oz ≈ 1.9 L) that ignores body size. For bigger people or hot days it falls short; for smaller people it can be too much.

When to drink more

• Exercise: add ~17–34 oz (0.5–1 L) per hour of training;
• Heat and humidity: sweat losses climb fast;
• Fever, diarrhea or vomiting: replace lost fluids;
• Pregnancy and breastfeeding raise needs.

Food counts too

Part of your hydration comes from food — fruit, soups, salads — and other drinks. Plain water should be the base, but total fluids are what matter.

The best gauge: urine color

Pale-yellow urine through the day usually means good hydration; dark yellow suggests drinking more. It's a more reliable signal than counting glasses.

FAQ

Do coffee and tea count? Yes. Coffee's diuretic effect at normal doses is small.

Can too much water be harmful? In extreme amounts over a short time, yes (hyponatremia). For most people it's rare — the body eliminates the excess.