Aug. 12, 2025

How Much Should You Drink After Rucking? The Science-Based Hydration Guide

Just finished a solid ruck and wondering how much you need to drink to properly rehydrate? You're not alone. Most ruckers either under-hydrate (and feel terrible the next day) or over-hydrate (and spend the evening running to the bathroom). In this comprehensive guide, I'll show you exactly how to calculate your post-ruck fluid replacement needs using evidence-based recommendations from the American College of Sports Medicine (ACSM).

Why Proper Post-Ruck Hydration Matters for Ruckers

Rucking is a unique beast when it comes to fluid loss. Unlike a quick gym session, rucking typically involves:

Extended duration (often 1-4+ hours)
Continuous movement with added weight
Outdoor conditions that increase sweat rates
Limited opportunities to drink during the activity

When you finish a ruck, your body isn't just thirsty, it's in a fluid deficit that affects everything from muscle recovery to your next training session. Poor rehydration leads to:

Prolonged fatigue and decreased performance
Increased muscle soreness and slower recovery
Higher risk of heat-related illness in future sessions
Compromised immune function
Poor sleep quality

The good news? There's actual science behind how much you need to drink, and it's based on something you can easily measure: your weight loss during the ruck.

The ACSM Weight-Based Hydration Formula for Ruckers

The American College of Sports Medicine provides clear guidance on post-exercise fluid replacement that's perfect for ruckers. Here's the science-backed approach:

The Basic Formula

Drink 150% of the fluid you lost during your ruck.

This translates to approximately 23 fluid ounces for every pound of body weight lost during your rucking session.

Why 150% Instead of 100%?

You might wonder why you need to drink more than you lost. Here's the deal:

Ongoing fluid losses: You continue sweating and losing fluid through breathing even after you stop rucking
Kidney function: Your kidneys continue producing urine during rehydration
Absorption efficiency: Not all the fluid you drink gets immediately absorbed and retained

The 150% replacement ratio accounts for these ongoing losses and ensures complete rehydration.

How to Calculate Your Post-Ruck Fluid Needs

Step 1: Weigh Yourself Before and After Rucking

The most accurate way to determine fluid loss is through pre- and post-exercise body weight measurement. Here's how to do it right:

Before Your Ruck:

Weigh yourself naked (or in minimal, dry clothing)
Use the same scale you'll use afterward
Empty your bladder first for accuracy

After Your Ruck:

Strip off all wet/sweaty clothing
Towel off excess sweat
Weigh yourself on the same scale

Step 2: Calculate Your Fluid Loss

Weight Loss (lbs) = Pre-Ruck Weight - Post-Ruck Weight

For example:

Pre-ruck weight: 180 lbs
Post-ruck weight: 177 lbs
Fluid loss: 3 lbs

Step 3: Determine Your Replacement Needs

Fluid Replacement = Weight Loss × 23 fl oz

Using our example:

3 lbs lost × 23 fl oz = 69 fluid ounces needed

That's about 8.5 cups or just over half a gallon of fluid.

Practical Post-Ruck Hydration Strategy

Timing Your Rehydration

Don't chug all that fluid at once. The ACSM recommends spreading your rehydration over several hours:

Immediate (First 30 minutes):

Drink 25% of your calculated needs
In our example: ~17 fl oz

First 2 Hours:

Drink 75% of your calculated needs
In our example: ~52 fl oz total

Complete Rehydration:

Finish remaining fluid over 4-6 hours
Monitor urine color as a hydration indicator

What Should You Drink?

For most rucking sessions under 2 hours, water works fine. But for longer rucks or hot conditions, consider:

Plain Water: Perfect for rucks under 90 minutes in moderate conditions

Sports Drinks: Better choice for:

Rucks longer than 90 minutes
Hot, humid conditions with high sweat rates
When you've lost more than 2-3% of body weight

Advanced Hydration Monitoring for Serious Ruckers

Using Urine Color Charts

The simplest way to monitor hydration status:

Pale yellow (lemonade color): Well hydrated
Dark yellow (apple juice color): Dehydrated
Clear: Possibly over-hydrated

Sweat Rate Calculations

For ruckers who train frequently, calculating your individual sweat rate helps with planning:

Sweat Rate Formula: (Pre-weight - Post-weight + Fluid consumed during ruck) ÷ Exercise duration = Sweat rate per hour

This helps you understand your individual fluid needs for different conditions.

Listen to The Rucker's Edge Podcast for More Hydration Strategies

Want to dive deeper into rucking hydration timing and performance optimization strategies?

➡️ Listen on Apple Podcast

➡️ Listen on Spotify

Disclaimer

I'm not a medical professional. This post reflects evidence-based guidelines from the American College of Sports Medicine but should not replace individualized medical advice. Please consult your doctor, sports nutritionist, or certified fitness professional before making significant changes to your hydration strategy...especially if you have underlying health conditions or take medications that affect fluid balance.

Final Thoughts on Post-Ruck Hydration

Proper rehydration isn't just about quenching your thirst, it's about optimizing recovery and preparing your body for the next challenge.

The beauty of the weight-based approach is its simplicity and accuracy. No guessing, no generic recommendations that might not fit your situation. Just step on the scale, do some quick math, and drink accordingly.

Once you dial in your individual needs, post-ruck hydration becomes second nature.

Your scale doesn't lie, and neither does science. Use both to your advantage.

Ruck on (and hydrate smart),

Spencer

Host of The Rucker's Edge Podcast

Photo by Anderson Rian on Unsplash