Weigh yourself before and after one session, enter three numbers, and get your personal sweat rate plus a sodium target you can match to any product. Math, not medical advice.
Not medical advice. This tool estimates fluid and sodium losses from your own weigh-in data. If you take diuretics or blood pressure medication, have kidney or heart disease, or follow a sodium-restricted diet, talk to your clinician before supplementing electrolytes.
Your session
Matching products to your sodium number
Servings per hour of sweating it would take to replace the sodium loss estimated above. Fractions mean one serving covers more than an hour.
| Product | Sodium / serving | Servings per hour |
|---|
Label numbers current as of August 2026. See the full comparisons: LMNT, Liquid I.V. vs LMNT, Nuun vs Ultima.
How to measure your sweat rate accurately
The protocol sports scientists use is simple enough to do at home. Weigh yourself nude or in dry minimal clothing on the same scale before and immediately after a session, towel off sweat first, and track every sip you drink in between. One kilogram of weight change equals about one liter of sweat; one pound equals about 15.3 fluid ounces. If you used the bathroom mid-session, the estimate loses accuracy, so pick a session where you did not.
Repeat the measurement in different conditions. Heat, humidity, intensity, and acclimation all shift your rate, often by half a liter per hour or more, so a summer outdoor number and an indoor winter number are two different baselines worth knowing.
What the sodium estimate means
Sweat sodium concentration varies person to person far more than sweat volume does; published ranges run from roughly 460 to 1,840 mg per liter. The saltiness selector maps visible signs (salt streaks, stinging eyes) to points inside that range, which makes your number an informed estimate, not a lab result. A wearable sweat-sodium patch or a lab sweat test is the only way to pin it down precisely.
Important caveats
Drinking far beyond your sweat rate is more dangerous than mild dehydration. Overdrinking plain water dilutes blood sodium and can cause exercise-associated hyponatremia; if the calculator shows you gained weight during a session, that is the warning to heed. Fluid targets during exercise exist to keep losses under about 2 percent of body weight, not to finish heavier than you started.
When to skip electrolyte products entirely
Sessions under an hour at easy effort, in cool conditions, are covered by water and your next meal. The math here matters for the long, hot, or salty cases; see the honest gates in our sport guides below.
Use your number in our sport guides
Your sweat rate is the input every hydration decision depends on. Apply it with the honest product picks in our guides for runners, cyclists, pickleball, tennis, golf, hiking, hot yoga, and outdoor work, or go deeper with the complete electrolyte guide and the electrolyte replacement calculator.
