Race Hydration Calculator
Estimate fluid and sodium needs for a race from duration and heat.
Quick answer: enter your details below and click Plan My Hydration — your result appears instantly, right here in your browser. Nothing you enter is uploaded or stored.
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How to use
- Enter your weight and race duration.
- Pick the conditions you expect.
- Click Plan My Hydration.
About this tool
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.
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.