Race Hydration Planner: Fluids and Sodium for Race Day
Thirst alone is a late signal in a long race. A rough fluid and sodium plan, built from duration and heat, keeps drinking deliberate instead of random.
What is the Race Hydration Calculator?
Enter your weight, race duration, and conditions. The tool estimates sweat losses with a simple rate per hour that rises with heat, then totals fluid and a sodium range. This is an estimate and a planning guide, not medical advice; individual sweat rates vary widely.
How to use it
- Enter your weight and race duration.
- Pick the conditions you expect.
- Click Plan My Hydration.
Worked example
Over 4 hours in hot conditions at an estimated 900 ml per hour, fluid loss is about 3600 ml, with a suggested intake range of about 2520 to 3600 ml.
How much fluid does a 4-hour hot race lose?
About 3.6 litres at an estimated 900 ml per hour, though real sweat rates vary a lot between runners.
Frequently asked questions
Should I drink the full loss?
Most runners aim to replace much but not all of it; drinking far beyond losses carries its own risks.
Why does heat matter so much?
Sweat rate climbs sharply with temperature and humidity, so the same race can need very different fluid plans.