How much sodium is in your sweat?
Sweat sodium concentration typically runs ~900–2,000 mg per liter. Sweat rate typically runs ~0.5–2.5 L per hour. Multiply, and hourly losses land anywhere from ~450 mg to ~5,000 mg — a 10× spread across athletes. This is why the same sports drink works for one runner and doesn't for another.
Get your number →Typical ranges by sport & condition
| Activity | Sweat rate | Salt loss / hr |
|---|---|---|
| Light cycling, cool room | ~0.5 L | ~450–900 mg Na |
| Yoga, hot studio | ~1.0–1.5 L | ~900–2,700 mg Na |
| Distance running, mild heat | ~1.0–1.5 L | ~900–2,700 mg Na |
| Marathon, hot & humid | ~1.5–2.5 L | ~1,800–4,500 mg Na |
| Ultra / long ride in heat | ~1.5–2.5 L+ | ~1,800–5,000 mg Na |
Directional. Individual variation is large — the point of the calculator is that your body's number probably isn't any of these; it's yours.
Potassium and magnesium — the smaller numbers
Sweat also carries potassium and magnesium, but at smaller levels:
- Potassium — sweat concentration is typically ~200–400 mg per liter, which works out to roughly 29% of your sodium loss as a rule of thumb. Most pre-mixed sports drinks include some; many are light on it.
- Magnesium — sweat carries very little (~5–15 mg/L), but a small daily supplement (~300 mg) supports muscle function on longer efforts. Not a per-hour replacement number, more a daily baseline.
Why the calculator beats a table
Tables like the one above are averages for average sweaters. Two people running the same marathon in the same weather can differ by 2–3× in sodium loss. If you're a light sweater, most tabs give you too much. If you're a heavy sweater, they give you a third of what you need.
The calculator asks four things — your sport, your duration, your intensity, and your sweat saltiness — and outputs your target in Na, K, and Mg per hour. Or you can weigh in before and after a session and get the exact number for that specific workout.
What to do with your number
- Compare it against your current drink's label. The gap is usually surprising.
- Build a mix that hits it. A base sports mix plus a pinch of salt, KCl, and Mg costs about $1.50–$2 per session — versus $6.50 for premixed tabs formulated for the average.
- Test on one long effort. On-body proof, then adjust.
The full DIY build walks through it in six moves — or compare every electrolyte product by cost per 1,000 mg.