You will need a reliable scale to do these calculations. By reliable, we mean a scale that returns the same weight if you weigh yourself several times in a row. We strongly suggest a digital scale. Using Wal-Mart prices as an example, a digital scale weighing to 0.2lbs may be had for about $20; one weighing to 0.1lbs is in the $30 range. The scale weighing to 0.1lbs is the best choice; 0. lbs will do. A scale weighing to 0.5 lbs is insufficiently accurate.
Weigh yourself naked before exercising, and again, naked, on cessation. We suggest a minimum period of one hour for this test. To obtain your sweat rate, deduct finishing weight from starting weight, add ounces of fluid drunk and deduct ounces of urine passed (so you can see it might be a good idea not to pee during the test as, if you do, you will have to collect your urine and measure it).
| Starting weight | lbs | |
| Less: Ending weight | ( ) |
lbs |
| Weight lost | lbs | |
| Multiply by 16 to obtain weight lost in ounces |
ozs | |
| Add: Liquid consumed | ozs | |
| Less: Urine passed | ( ) |
ozs |
| SWEAT RATE PER PERIOD | ozs |
If you exercised for an hour, this is your hourly sweat rate. If you exercised for more than an hour, then correct the calculated weight to an hourly value.
We strongly suggest that if you are a Multisport athlete that you check sweat rate for all the sports you participate in. Your sweat rate while swimming will be significant, but typically less than you experience while running and cycling  roughly one-third and one-half respectively  although this will vary with water temperature and whether you are wearing a wetsuit.
You should generally try to rehydrate at, or slightly below your calculated sweat rates. You should NOT rehydrate above your calculated sweat rates. For more information request a copy of the Masters Athletic Performance advanced competitive rehydration protocol
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