The body-weight estimate that drives the sodium calculator is a population average. Some athletes sweat 30% more than the estimate, some 30% less. A 60-minute weigh-in test gives you your real number and replaces the guess with data.
Pre-weight, post-weight, and the ounces of fluid you drank are enough. We convert it to a measured sweat rate, grade it against the body-weight model, and hand it off to the sodium calculator with one click.
Hydration Audit
Convert a weigh-in test into a real sweat rate. Three numbers in, a validated mL/hr out, and a one-click handoff into the sodium calculator.
Not Medical Or Nutrition Advice
This calculator and the resulting plan are educational only. Endurance sports carry inherent risks and individual nutrition needs vary. Athletes should consult a qualified healthcare professional or a registered sports dietitian before applying any nutrition, hydration, or supplementation strategy, especially if you have a medical condition, are pregnant, take medications, or are training through injury. Use this information at your own risk.
How The Math Works
The sweat-loss equation is just conservation of mass. You started the session at one weight, ended at another, and put fluid into the system during the session. Whatever weight you lost plus the volume of fluid you drank equals the volume of sweat that left your body.
One pound of body weight equals roughly 16 fluid ounces, which is about 473 mL. We convert pre and post weights to kilograms, multiply by 1000 to get mL of water, add the fluid you consumed, and divide by session minutes to get a rate per hour.
The variance grade compares your measured rate against the ACSM body-weight model used by the sodium calculator by default (roughly 10 mL per kg of body weight per hour at race intensity, scaled by climate). A 10% match means the default math fits you; a 30% miss in either direction means you should use the measured value going forward.
For best accuracy: weigh nude or in identical dry kit, do the test at race effort and in race-day climate, and tally fluid consumed by counting bottle refills rather than guessing.
Sodium Handles Fluid Retention.
Nitrate Handles Oxygen Efficiency.
These are different physiological systems and both matter on race day. Build your sodium strategy with this calculator, then stack Beetroot Pro for the oxygen efficiency layer. The two are additive.