What this tool does
A practical starting target: about 35 ml per kilogram of body weight, plus 350 ml per 30 minutes of exercise, plus 500 ml if you marked hot. Sex is collected for context with other tools; the millilitre math here is driven by weight, exercise, and climate. Food moisture still counts toward the total.
How it works
DRI adequate intakes (about 2.7 L women / 3.7 L men from all fluids and food in U.S. tables) are a different construct. This page is a body-size heuristic plus sweat add-ons. It will not dose hyponatremia risk for ultra events and will not “flush toxins.”
Formula and methodology
ml/day ≈ 35 × weight(kg) + (exerciseMinutes / 30) × 350 + (hot ? 500 : 0). 35 ml/kg is a clinical rule of thumb, not a DRI. Exercise add-on is a round sweat replacement guess. Long hot sessions may need sodium as well as water — not modeled here.
How to interpret the result
Pale-straw urine and normal thirst beat chasing an extra litre because a bottle brand said so. Dark urine, dizziness, or no urine is a different problem. Forcing gallons can be dangerous. Caffeine-containing drinks still contribute fluid for most people.
Example
70 kg, 60 minutes training, temperate: 2,450 + 700 = 3,150 ml (about 3.2 L) from the heuristic. Hot climate adds 500 ml. If that person also eats a lot of fruit and soup, they may drink less from the tap and still land near the total.
Common mistakes
- Chugging this volume in two hours.
- Ignoring electrolytes on multi-hour sweaty work.
- Counting only plain water and then doubling the target.
- Using this as a detox protocol.
When this estimate may be off
- Heart, kidney, or SIADH conditions that restrict fluid.
- Ultra-endurance or military heat labs that need sweat-rate testing.
- High altitude or fever — not in the formula.
- Very high or very low body weights where 35 ml/kg mis-scales.