Hydration Calculator
Find your sweat rate and a before, during, and after fluid plan for your workouts
Your Workout
About the Hydration Calculator
This Hydration Calculator estimates how much fluid your body loses through sweat during exercise and turns that into a practical before, during, and after drinking plan. Staying on top of hydration helps protect your performance, focus, and safety — losing more than about 2% of your body weight as fluid can measurably reduce endurance and strength.
The Measure method is the most accurate: by weighing yourself immediately before and after a workout (and adding any fluid you drank), it works out your true sweat rate. The Estimate method is handy when you don't have a scale — it predicts your sweat rate from exercise intensity and climate instead.
Sweat Rate
The amount of fluid you lose per hour of activity. It rises with effort, heat, and humidity and varies a lot from person to person.
Climate Matters
Hot and humid conditions can more than double your sweat losses compared with cool weather, so your fluid needs scale up too.
How to Use This Calculator
- Choose your preferred units — metric or imperial.
- Pick a method: Measure if you can weigh yourself before and after, or Estimate if not.
- For the measure method, weigh yourself with minimal clothing right before and right after exercise, then enter both weights, any fluid you drank, and the duration.
- For the estimate method, enter your weight, workout length, intensity, and the climate you train in.
- Click Calculate Hydration to see your sweat rate and a full fluid plan.
- Use the before, during, and after targets to plan your drinking for similar sessions.
Frequently Asked Questions
How is sweat rate calculated?
In the measure method, sweat loss equals your weight loss during exercise plus any fluid you drank (since 1 litre of water weighs about 1 kg). Dividing that by the exercise duration gives your sweat rate per hour. The estimate method instead predicts your rate from typical values for your intensity and climate.
Why does losing 2% of body weight matter?
Research suggests that once fluid losses pass roughly 2% of body weight, endurance, strength, and concentration begin to decline. Keeping losses below that level during exercise helps you maintain performance and feel better.
How much should I drink after exercise?
A common guideline is to replace about 150% of the fluid you lost over the next few hours. The extra accounts for ongoing losses through urine and continued sweating during recovery.
Can I just drink water, or do I need electrolytes?
For short, easy sessions, water is usually enough. For workouts longer than 60–90 minutes, heavy sweating, or hot weather, adding electrolytes (especially sodium) helps you absorb and retain fluid and reduces the risk of low blood sodium.
Is this a substitute for medical advice?
No. This calculator gives general fitness guidance based on common sports-science guidelines. Individual needs vary, and conditions like heart, kidney, or sodium-balance issues require personalized advice from a healthcare professional.