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How to calculate how much water you should drink

Byline: Jennifer Stone, PT, DPT, OCS, Clinic Supervisor

Summer is right around the corner … and with it, summer activities, warmer temperatures and an increased risk for dehydration. Here are some tips to help you make sure you are drinking enough fluids to maintain good levels of hydration.

You are probably all aware of the “cardinal rule” that says adults should drink six to eight 8-ounce glasses of water per day. The truth is, this is an estimate and the actual amount you should be drinking per day can vary quite significantly. There are multiple factors that can impact how much water you should be drinking.


Your weight is one variable that changes the amount of water you should be drinking. To help you establish a baseline, you can use the following rule-of-thumb equation described in U.S. News & World Report.

Weight calculation

In short, the equation tells you to take half your body weight, and drink that amount in ounces of water. In the example, notice that you should be drinking more than 12 glasses of water, not eight!


Your exercise habits affect the amount of water you should be drinking, as well. The American College of Sports Medicine recommends adding 12 ounces of water to your daily intake for every 30 minutes that you plan to work out.

Water exercise calculation
If you are exercising outside and it is very hot, you may need to add more.

Special considerations

There are several special considerations to maintaining a healthy hydration level. If you are pregnant or breastfeeding, you need to increase your fluid intake by 24 to 32 ounces depending on how much you weigh, according to the American Pregnancy Association. It is also important that you get a lot of your hydration from water. If you are primarily drinking sodas or caffeinated beverages such as coffee or tea, you do not get as much “bang for your buck” when it comes to fluid intake (i.e., they don’t “count” as much).

Rules of thumb

The good news is there are some fairly easy rules of thumb to follow when it comes to hydration. One of the important ones is to pre-hydrate. In other words, drink BEFORE you start feeling thirsty, or BEFORE you do an activity. Going running? Drink several glasses of water before you start. Thirst is actually a sign of dehydration, so if you feel thirsty, you have some catching up to do!

Also, monitor your urine. If you are adequately hydrated, you should be urinating about once every two to four hours, and your urine should be colorless or a very pale yellow (the color of hay or lighter). If it is darker than that, you haven’t had enough fluid. Headaches and dizziness are a late sign of dehydration. If you start experiencing those, you really need to up the water intake, and quickly.

Dehydration can turn a fun summer activity into an unpleasant experience at best, or a trip to the emergency room at worst.

Don’t wait until it’s too late. Bring water bottles with you, and keep yourself and your family hydrated during your summer fun!

More info:

Sources cited:

About the author: Jennifer is a Clinic Supervisor for Mizzou Therapy Services (Rangeline location) and a board-certified specialist in orthopedic physical therapy. She is also CAP certified in women’s health physical therapy. She has five years of experience in physical therapy and earned her Master’s degree from Texas State University, her doctorate from Massachusetts General Hospital Institute for Health Professions, and completed an orthopedic residency through Evidence in Motion.

Reviewed 2022-05-06


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