How this calculation works
This is an illustrative fluid-planning calculation, not a validated personal drinking requirement. Go Calculator combines a weight allowance, a fixed activity allowance and an optional heat uplift so you can see the arithmetic. The cited CDC guidance explains why fluid needs vary; it does not prescribe this tool’s 35 mL/kg, 400 mL/hour or 10% coefficients.
Worked example
This example uses illustrative inputs. Your current result is shown above.
At 70 kg and 45 activity minutes, base = 70 × 35 = 2,450 mL and activity allowance = 45 ÷ 60 × 400 = 300 mL. Without heat uplift, total = 2,750 mL or 2.75 L. Turning on heat uplift adds 275 mL, giving 3,025 mL or 3.03 L after rounding.
Assumptions and limits
- These coefficients are explicit Go Calculator planning assumptions, not an official CDC or USDA intake equation and not a clinical fluid prescription.
- Fluid also comes from foods and other drinks. Do not interpret the result as extra plain water to drink on top of everything else, or force yourself to meet it.
- Sweat losses, activity intensity, humidity, pregnancy, breastfeeding, illness and kidney or heart conditions are not modelled. A clinician’s fluid restriction or individual guidance takes priority.
Questions people ask
Is 2.75 litres a precise amount I must drink?
No. That precision comes from arithmetic, not knowledge of your body’s needs. Treat it as an illustration, and consider food, other drinks, conditions and any medical guidance.
Where do the 35, 400 and 10% values come from?
They are the fixed assumptions used by this calculator. We do not claim that the linked public-health guidance validates this particular formula.
Does the heat switch measure my sweat loss?
No. It adds a fixed 10% to the base-plus-activity amount. Actual sweat loss can vary widely, so this is not an exercise hydration protocol.