Water intake calculator.

A sensible daily hydration range for your body and your day — sized to your weight, bumped for training and heat, and honest about the fact that “eight glasses” was never science.

Based on the widely used guideline of roughly 30–35 ml of fluid per kg of body weight per day, with an extra 0.5–1 liter for exercise and heat. It’s a practical rule of thumb, not a measured medical requirement — food supplies part of your fluid too. Guidance, not medical advice; kidney or heart conditions change the picture, so ask your doctor.

Hydration myths worth dropping

Few health rules are repeated as confidently — and sourced as thinly — as the ones about water. Two corrections make hydration much less stressful:

• “Eight glasses a day” is folklore, not physiology. The figure traces back to a 1940s recommendation that also noted most of that fluid comes from food — a caveat that got lost in the retelling. Actual needs vary with body size, activity, climate and diet, which is why a weight-based range beats a universal number.
• For most healthy people, thirst is a decent guide. Your body regulates fluid tightly and asks when it needs more. The main exceptions are hard training in heat and older adults, whose thirst signal weakens — situations where drinking on a schedule genuinely helps.

A practical middle ground: use the range above as your day’s ballpark, drink when thirsty, and glance at urine color — pale straw means you’re fine. Remember that soup, fruit, coffee and tea all count toward the total; food alone typically covers around a fifth of it.

Tracking water where you already track meals

Hydration habits stick when they live next to an existing habit instead of in a separate app. Cal AI: Calorie Scanner logs water alongside your meals — snap the plate, tap the glass, and both totals build through the day on the same screen.