Sweat Rate Calculator
Quick answer: Sweat rate = (pre-exercise weight − post-exercise weight + fluids consumed) ÷ hours. Losing 1.5 lb while drinking 32 oz over 1.5 hours = 3.5 lb ÷ 1.5 = 2.33 lb/hr — about 37 oz/hr (1.1 L/hr).
Weigh yourself before and after a workout, note what you drank and how long you trained, and this sweat rate calculator converts it into fluid loss per hour — the key number for planning a hydration strategy.
Enter your numbers
Weigh in the same minimal clothing both times, towel off sweat first.
Your results
| Sweat rate | 2.33 lb/hr |
|---|---|
| Fluid loss | 37.3 oz/hr |
| Fluid loss | 1,104 mL/hr |
| Suggested hourly fluid replacement | ≈37 oz/hr (estimate) |
Estimate — it ignores bathroom breaks and metabolic water. General information only, not medical advice.
How to use this calculator
Empty your bladder, weigh yourself in minimal clothing before the workout, and write the number down. Train for a known time at your normal effort, tracking every ounce you drink. Right after, towel off and weigh yourself again in the same clothing.
Enter all four numbers and the calculator does the rest. Repeat the test in different conditions — hot days, cool days, easy and hard sessions — since sweat rate shifts with heat, humidity, and intensity.
How it works
Sweat (lb) = (weight before − weight after) + fluids consumed in lb (oz ÷ 16). Rate = sweat ÷ hours. Convert: oz/hr = lb/hr × 16; mL/hr = oz/hr × 29.5735. This is an estimate — it ignores urine loss and metabolic water.
The math rests on one fact: short-term body-mass change during exercise is almost entirely water. Each pound of body weight lost equals about 16 fluid ounces of sweat, so adding back the fluids you drank accounts for everything you sweated out.
Worked example
160 − 158.5 = 1.5 lb lost; 32 oz = 2 lb fluid → 3.5 lb total ÷ 1.5 hr = 2.33 lb/hr = 37.3 oz/hr = 1,104 mL/hr.
Reference data
There is no external dataset behind this tool — it is a pure formula. The standard constants used are: 16 oz per lb (fluid weight) and 29.5735 mL per oz. Sports-science sources note most endurance athletes lose between 0.5 and 1.5 liters (16–48 oz) of sweat per hour depending on body size, intensity, heat, and humidity.
Source: Precision Hydration — "How to measure your sweat rate" (2026).
Method & sources
Total sweat equals the body-mass lost on the scale plus the weight of any fluid consumed, converted with the standard fluid-weight constants. Dividing by session hours gives the rate. It is an estimate because urine loss during the session and metabolic water production are not measured.
Frequently asked questions
Why weigh myself before and after?
Short-term weight change during exercise is almost entirely fluid loss, so the scale gives a direct sweat measurement.
Should I drink exactly my sweat rate?
Matching it is a reasonable starting target for long sessions. This is general information, not medical advice — adjust for heat, intensity, and how you feel.
What should I wear for the weigh-ins?
Weigh in the same minimal clothing both times so sweat-soaked gear does not distort the numbers.
How accurate is this?
It is an estimate. It ignores bathroom breaks and the small amount of water produced by metabolism.