I'm a trail runner training for my first 100K. I'm not fast, I'm not sponsored, I'm not coaching anyone. I'm just a guy who likes long days in the mountains and is willing to suffer to finish what he started.
I'm also a heavy sweater. The kind where my shirt is crunchy with salt after a summer long run and my eyes sting two hours in. For years I bought the fancy electrolyte powders — LMNT, Skratch, Precision, the works — and watched my training budget bleed out at $2 to $3 per serving. At 42 miles a week and climbing, that math gets ugly fast.
One Sunday I looked at the back of an LMNT packet, then at a $9 bag of potassium chloride on Amazon, and the gap was absurd. So I sat down with a kitchen scale and a few sports-science papers and worked out my own formula. It works better than the pre-mixes — because it's calibrated to me — and it costs about a quarter per bottle. That calculator is what this site is.
Outside of running I ski — alpine when I'm at a resort, backcountry when the snow and the weather and the legs all agree — and I'm extremely good at sitting around the house. None of those things will get me to 100K. The training will. And the training only goes well when I don't blow up from under-fueling in the heat (or, in winter, when I bonk halfway up a skin track because I forgot to eat).
Replacement targets in the calculator are deliberately conservative. I'd rather undershoot than send anyone to the hospital for over-drinking.
The big risk in endurance hydration is exercise-associated hyponatremia — low blood sodium from drinking too much water. It kills people. Slight under-replacement is mild and self-correcting; over-replacement plus over-drinking is the dangerous one. The targets above keep most adult athletes in the green zone in most conditions. Drink to thirst.
If you find a math error, a stale citation, a weird edge case in the calculator, or you just want to talk about trail running — please write. I'll fix the bug and credit you. I'm a real person, not a chatbot.