Sweat Rate Calculator – Measure Fluid Loss Per Hour
Sweat Rate Calculator
Measure your exercise sweat rate from a real before-and-after weigh-in, accounting for fluid consumed and urine passed. Results are shown in litres/hour, mL/hour and fluid ounces/hour.
Measured, not guessed. Sweat rate changes with heat, humidity, intensity, clothing, acclimatization and the individual, so repeat the test in conditions similar to your training or event.
Medically reviewed
MBBS • MD (Pathology) • Professor — Department of Pathology, Jawaharlal Nehru Medical College, Aligarh Muslim University (A.M.U.), Aligarh, India
Reviewed this Sweat Rate Calculator for the pre/post body-mass method, fluid and urine adjustments, sweat-rate interpretation, optional sodium-loss calculation, exercise safety guardrails, and limitations.
View full medical reviewer profile →Your Sweat Test
Advanced: measured sweat sodium
Your Results
Assumptions & Warnings
Use the calculated sweat rate in the Exercise Hydration Calculator for before/during/after planning.
Open Exercise Hydration Calculator →📊 Sweat-Test Fluid Balance
This graph compares measured sweat loss with fluid consumed and the net scale-weight change during the session.
🧮 Sweat Rate Formula & Calculation
This is the field equation published in the National Athletic Trainers’ Association position statement. One kilogram of acute body-mass change is treated approximately as one litre of water for this field calculation.
📋 Detailed Result Breakdown
| Item | Your result |
|---|---|
| Enter a complete test. | |
⚠️ Limitations & Test Quality
Your sweat rate is not a permanent personal constant. It can change with temperature, humidity, intensity, fitness, heat acclimatization, clothing and equipment. Repeat testing under conditions similar to those you want to plan for.
Body-mass change is most useful over relatively short exercise periods. Long endurance events introduce additional body-mass changes from fuel use and metabolic water, so the simple weigh-in method becomes less exact.
If you have a history of exercise-associated hyponatraemia, heat illness, kidney/heart disease or another condition affecting fluids/electrolytes, use professional sports-medicine guidance rather than an online result.
Questions People Ask About Sweat Rate
How do I calculate my sweat rate?
Weigh yourself before and immediately after exercise, add the fluid you drank, subtract any urine passed, and divide the resulting sweat loss by exercise time in hours.
What is a normal sweat rate per hour?
There is a very wide range. The NATA position statement reports adult exercise sweat rates from about 0.5 to 4.0 L/hour in the literature it reviewed. Your own number should be measured in representative conditions instead of compared rigidly with an average.
Does 1 kg of weight loss equal 1 litre of sweat?
For a short field sweat test, approximately yes: the standard equation treats a 1 kg acute body-mass change as roughly 1 L of water, while also accounting for drinks and urine.
Should I replace 100% of my sweat loss during exercise?
Not automatically. NATA recommends individualized intake that approximates personal losses while avoiding both excessive dehydration and overconsumption. People should not gain body weight from overdrinking during exercise when they started hydrated.
What does 2% body-weight loss mean?
Sports hydration guidance often uses about 2% body-mass loss as a practical threshold to avoid during exercise when performance and safety are priorities. For a 70 kg athlete, 2% is 1.4 kg.
How long should a sweat-rate test be?
A session long enough to create a measurable change is useful; many field protocols use roughly 45–90 minutes. Consistency of weigh-ins and representative conditions matter more than chasing one exact duration.
Does sweat rate change in hot weather?
Yes. Sweat rate can change with heat, humidity, intensity, clothing and acclimatization. Repeat the test in hot conditions if that is where you will train or compete.
Can this calculator estimate sodium loss?
Only if you enter a measured sweat-sodium concentration in mg/L. The calculator multiplies that concentration by measured sweat volume. It does not guess sodium concentration from symptoms or prescribe how much sodium to consume.
📚 Sources & Research
- National Athletic Trainers’ Association Position Statement: Fluid Replacement for the Physically Active (2017) — sweat-rate equation, individualized plans, body-mass guardrails and post-exercise replacement.
- American College of Sports Medicine Position Stand: Exercise and Fluid Replacement (2007) — individualized sweat-rate assessment and prevention of excessive dehydration/overdrinking.