The 0.67 Rule: Exactly How Many Ounces of Water Should You Drink?

For decades, Americans have been told to drink "eight 8-ounce glasses of water a day." While 64 ounces is easy to remember, it's not a one-size-fits-all rule. A 120-pound sedentary office worker and a 200-pound athlete living in hot, sunny Florida have vastly different hydration needs!

Modern health experts and dietitians recommend a more personalized approach: The 0.67 Rule.

Here is a complete guide on how to calculate exactly how many ounces of water you should drink daily for optimal health, clear skin, and a fast metabolism.

What is the 0.67 Rule?

The 0.67 rule states that a person should drink roughly two-thirds (or 67%) of their body weight in ounces of water every single day, just as a baseline.

The Math:

1. Find your weight in pounds (lbs).
2. Multiply that number by 0.67.
3. The result is your daily baseline water intake in ounces.

Example: If you weigh 150 lbs, the calculation is 150 × 0.67 = 100.5. You should be drinking roughly 100 ounces of water a day as a baseline.

If you don't want to do the math by hand, you can enter your weight into our free Water Intake Calculator to get your exact ounce recommendation instantly.

Adjusting for Exercise

The 0.67 rule only gives you a baseline for a normal, sedentary day. If you exercise, sweat, or spend time outdoors in hot climates, your body loses water much faster, and you must compensate for it.

The general rule of thumb from the American College of Sports Medicine is to add 12 ounces of water for every 30 minutes of physical activity.

Example: If our 150-pound person (baseline of 100 ounces) goes for a 45-minute run, they need to add roughly 18 ounces to their daily total. Their new goal is 118 ounces for that day.

How to Track Your Ounces

Tracking ounces can feel tedious if you're drinking out of random cups all day. The easiest way to hit your goal is to buy a reusable water bottle that lists its capacity in ounces (such as a 32 oz Nalgene or a 40 oz Hydroflask).

If your goal is 100 ounces a day, and you have a 32 oz water bottle, you simply know you need to fill and finish that bottle three times throughout the day to hit your target.

Why is Precise Hydration So Important?

Even mild dehydration can cause noticeable symptoms, including:

• Brain fog and afternoon fatigue.
• Slower metabolism and false hunger cues (often, when you feel hungry, your body is actually just thirsty).
• Dry skin and accelerated aging.
• Muscle cramps during workouts.

By throwing out the old "8 glasses" myth and using a personalized calculation based on your actual body weight, you ensure your body gets exactly what it needs to perform at its best.

Ready to find your number? Use our Interactive Water Intake Calculator to get a precise recommendation tailored to your weight, gender, and exercise routine!