Calculate triathlon race nutrition: total carbs, fluid and sodium from your race time and hourly targets, or your sweat rate from a test session.
How the Race Nutrition Totals Work
The calculator multiplies explicit hourly targets by duration. Carbohydrate total equals grams per hour times hours. Fluid total equals liters per hour times hours. Sodium per hour equals fluid liters per hour times sodium concentration in milligrams per liter; multiplying again by duration gives total sodium.
| Exercise duration | Carbohydrate reference | Planning note |
|---|---|---|
| Under about 1 hour | No fixed hourly target | Small amounts or a mouth rinse may be used during sustained high intensity |
| 1 to 2.5 hours | 30–60 g/h | Practice the product and timing used in competition |
| Longer than 2.5 hours | Up to 90 g/h | Higher rates require practiced tolerance and multiple transportable carbohydrates |
Why Body Weight Does Not Set the Plan
During-event carbohydrate guidance is driven mainly by duration and intensity. Fluid depends on sweat rate, conditions, and tolerance. Sodium depends on fluid volume and sweat sodium concentration. Body mass is therefore used only to provide grams-per-kilogram-per-hour context and to support the sweat test; it does not generate the three targets automatically.
Sweat-Rate Formula
Sweat loss in liters equals pre-exercise mass in kilograms minus post-exercise mass, plus fluid consumed in liters, minus urine in liters. Divide by test hours for liters per hour. The calculation treats one kilogram of acute mass change as approximately one liter of water.
Worked Examples
A five-hour plan at 75 g carbohydrate per hour, 650 mL fluid per hour, and 600 mg sodium per liter produces 375 g carbohydrate, 3.25 L fluid, and 1,950 mg sodium. At a 750 mL bottle size, that is 4.333 bottle volumes, so five whole bottles are required to carry at least the calculated volume.
For a field test starting at 70 kg and ending at 69.2 kg with 0.75 L consumed, 0.10 L urine, and 1.5 hours elapsed, sweat loss is 1.45 L and sweat rate is about 0.9667 L/h. An explicitly selected 80% scenario is about 0.7733 L/h.
Fluid and Sodium Context
A general 0.4–0.8 L/h range can be a starting reference, but measured losses and tolerance take precedence. Sodium concentration remains editable rather than being presented as a universal dose. The compact first release reports race totals rather than assuming intake during the swim or inventing discipline-specific rates.
Assumptions and Limitations
Targets must be practiced. Heat, humidity, intensity, body size, gastrointestinal tolerance, access to aid, product concentration, and sweat sodium can change needs. Do not force fluid beyond losses or tolerance; overdrinking can be harmful. Repeat sweat tests in conditions resembling the race and use race-day logistics to refine the plan.
Sources
Thomas, Erdman, and Burke, Nutrition and Athletic Performance, 2016. Burke et al., Carbohydrates for Training and Competition, 2011. McDermott et al., National Athletic Trainers' Association Position Statement: Fluid Replacement for the Physically Active, 2017. Racinais et al., IOC Consensus Statement on Recommendations and Regulations for Sport Events in the Heat, 2023.
