Tools / Calculator 05
Water Intake Calculator.
Daily fluid target by body weight, training, and climate. Liters or fluid ounces, with the sources behind the math.
Daily target
—
| Baseline (body weight) | — |
| Training adjustment | — |
| Climate adjustment | — |
| Total target | — |
How it's calculated.
- Baseline. 35 ml × body weight in kg (≈ 0.5 fl oz × lb). A common clinical estimate; falls roughly inside the IOM Adequate Intake bands for sedentary adults.
- Training adjustment. +500–1500 ml per hour of training, scaling with intensity. Fluid loss in sweat is highly individual; if you weigh before and after a session, a 1 kg drop ≈ 1 L of replacement.
- Climate adjustment. Hot or humid: +500 ml; cold & dry (heated indoor air): +250 ml. Heated indoor environments dehydrate quietly — the air is dry and you don't notice the loss.
Sources: Institute of Medicine, Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. Washington, DC: National Academies Press, 2005. ACSM Position Stand: Exercise and Fluid Replacement. Med Sci Sports Exerc, 2007; 39(2):377–390.
Things this calculator doesn't know.
- Your sweat rate. The simplest measurement: weigh yourself naked before and after a one-hour training session (no fluids during). The difference in kilograms is roughly the liters you lost. Replace it.
- Electrolytes. Drinking large volumes of plain water during long sessions or in heat without sodium is the classic hyponatremia mistake. If sessions are over 90 min in heat, add electrolytes.
- Medication and condition adjustments. GLP-1s, SGLT2 inhibitors, diuretics, and several others change fluid balance. Defer to your clinician's specific guidance.
- Urine color is the cheap sensor. Pale straw = good. Apple juice = catch up. Dark amber = behind. Two free data points per visit to the bathroom.