Knowing how much fluid you lose during exercise or a heat session helps you rehydrate properly instead of guessing. This calculator estimates your sweat loss and gives a simple rehydration target based on your before and after weight.

Sweat Loss Calculator





How this calculator works

Each pound of body weight lost during activity is roughly equal to 16 fluid ounces of sweat. Adding back any fluid you drank during the session gives a more accurate total sweat loss. The rehydration target uses a common guideline of replacing about 150 percent of fluid lost, since some of what you drink is processed and excreted rather than retained.

Frequently asked questions

Why weigh in before and after instead of just tracking water intake? Body weight change accounts for fluid lost through sweat that was not replaced during the session, giving a more complete picture than intake alone.

Does this apply to sauna and hot yoga too? Yes, the same before and after weight method works for any activity or heat exposure that causes significant sweating.

Should I weigh myself with clothes on? Weighing in similar, minimal clothing both times gives a more accurate reading. Wet clothing after a session should be accounted for or removed before the after weigh-in.

Is plain water enough for rehydration? For most everyday sessions, water is fine. For longer or hotter sessions with heavy sweat loss, adding electrolytes helps your body retain the fluid instead of losing it again quickly.

Can this calculator help with heat acclimation? Tracking your sweat rate over several sessions in similar conditions is a practical way to see your body adapting, since a lower sweat rate at the same heat exposure over time often reflects improved heat tolerance.

This calculator provides general wellness guidance based on commonly referenced recovery and thermal therapy practices. It is not medical advice and does not replace consultation with a qualified healthcare provider. If you have any cardiovascular condition, are pregnant, or have other health concerns, consult your doctor before starting sauna, cold plunge, or ice bath practices.