tale of two measurements

A tale of two measurements: Fluid ounces and net weight ounces

Say you’re shopping for a new car, but not just any car; you’re after a Ford. Fords have a sleek and cool style, something that you believe you embody yourself. The salesperson knows just what you’re talking about. Moments later, the car-shopping vibe fizzles as a 1984 Fiesta sputters to a stop in front of you. Hey, it’s a Ford, isn’t it? The details got lost in translation. Don’t make the same mistake with your product’s volume and/or weight declarations.

Meet Floyd and Natalie
Floyd drinks nothing but big gulps to stretch his stomach for his weekly one gallon milk chugging contest. A standard dairy bottle is his container of choice. Natalie on the other hand eats nothing but spinach leaves to maintain a “healthy” weight. According to her, the lighter a container is the better. Floyd thinks in terms of volume or fluid ounces (FL. OZ.) while Natalie worries about weight (or for this illustrative purpose, net weight ounces, NET WT. OZ.). Settle the measuring score between fluid and net weight ounces before deciding on the right container for your product.

Fill up a fluid ounce container
The water you gulp after an intense workout and the energy drink you cling to the morning after a spontaneous late night on the town are both sold in fluid ounce capacities. The fluid ounce measurement assigned to a container is based on one thing, volume; referring to the amount of storable space inside the container.

Weigh down a net weight ounce container
Sugar, flour, honey, salt and… babies are all measured in net weight ounces, based on the weight of an item. When I hear that a newborn was delivered at 6 lbs. 8 oz, I’m aware that this measurement is based on net weight calculations. Otherwise I might throw thirteen cups of baking ingredients together, bake at 350°F for 9 minutes and hope to welcome my own pastry child into the world… maybe a gingerbread boy. Not only is this slightly disturbing, but more importantly, the formula is faulty. Also, don’t get gross weight and net weight confused. The gross weight of your bag of flour would mean you throw the entire thing on a scale and take that number. The net weight of your bag of flour means you subtract the weight of the bag. You don’t eat the bag.

The final word – Fluid ounces and net weight ounces aren’t equal
Take a look at the equation below. To a layman the numbers might seem like they add up.

glass container of molasses
The issue is that the two units of measure aren’t interchangeable. Fluid ounces are only concerned with volume, while net weight ounces focus on weight; two vastly different aspects of container measurements. 8 FL. OZ. of molasses doesn’t weigh 8 NET WT. OZ (it actually weighs 12 NET. WT. OZ.).

“F” is for fluid ounces and Floyd (remember him? He’s the guy who drinks from a high volume container). “N” is for net weight ounces and Natalie (the girl that never leaves home without a scale). Fluid ounces are to volume, as net weight ounces are to weight. Keep your container volume and/or weight declarations clear to avoid a Ford Fiesta-like fiasco.

How do you remember the difference between fluid and net weight ounces? Share your creative concepts in the comments!

18 thoughts on “A tale of two measurements: Fluid ounces and net weight ounces

      • Hi Robyn,

        I ran your question by our resident expert Jeff and here is what he had to say:

        To my knowledge there’s no reason you can’t list both weight and volume – except for certain items that are required to be labeled a certain way (honey, for example, is only sold by weight). That being said, I’ve never actually seen it done. In my personal opinion, I don’t see the benefit of doing that. A fluid oz is the amount of space taken up by 1 oz (by weight) of water – so in some cases it might be the same number anyway, especially if you have a product made mostly from water. To me, too many numbers might get confusing. Plus, how often have you been in the market for a pound of shampoo?

        Typically the only time I see more than one measurement is when both ml and fluid oz measurements are used (for example, a half-liter bottle of water will often say something like 0.5L (16.9 fl oz) since many people don’t understand the metric system.

  1. Hi Anonymous,

    That’s a great question. I would suggest labeling the product in fluid ounce (FL. OZ.) terms. It’s important to use specific volume or weight descriptions to clearly describe your product’s details. Thanks for posting!

  2. This blog is great help! I took home ec, in high school, and the teacher was SO adamant about not putting the powder items, we measured, in the fluid measuring cups and vice versa. That was when I learned that powders in oz are not the same as fluid in oz. Some people do not think it matters in baking, but it does. I have yet to not make a perfect cookie thanks to my home ec teacher 🙂 I also learned golden brown is burnt. haha!

  3. I look at a can of R134a AC refrigerant for your car and it actually say ‘Net Wt. 12 Fl. Oz (340 g)’. I believe they mean the weight of the refrigerant in the can is 12 ounces or 340 grams. They should not even have the contradicting term Fl in the description. Do you agree?

    • Hey John, thanks for the question. I actually believe that the can of refrigerant is including both measurements. The label is saying that there is 12 Fl. Oz of product in the can AND that it weighs 340 grams. Does that help?

      • I am not sure you are correct Steve. I searched for other cans at car quest and those cans left out the Fl. altogether. It is a mistake I believe and completely reflects why this blog topic is discussed in the first place. People don’t understand it – even marketers selling products! Back to the refrigerant – you are supposed to put an amount of refrigerant in your car based on weight. They don’t tell you how much based on volume. Hence the 12 Fluid ounces has no bearing on it. What is important is that you are buying 12 ounces (weight) or 340 grams of the product which are equivalent…

        • I agree John. Isn’t refrigerant in cans a gas? How would that be measured? I would think by weight not fluid weight? Because gas isn’t a fluid until the water in the air touches it. nt wt would probably be a better choice of labeling on a refrigerant. I read about refrigerant and someone suggested measuring it in Kg. It would be more accurate. They mentioned that oz and fl oz is confusing because it has the same term oz (which can confuse people). It might be helpful to have the containers that are sold show how many fl oz and oz they could hold instead of just fl oz. But because there are so many things that can go into containers I would say that most people should just sample the items they are wanting to try to know for sure if it will work for their product. Gas is a whole other level John 🙂 Good point though.

  4. Why doesn’t someone come up with a term other than “ounces” for either volume or weight? Using the same term for two different measures is nuts. Speaking of nuts, how much peanut butter is 8 ounces of peanut butter? A cup? A half-pound?

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