Why The Math On Your Soda Bottles & Cans Doesn’t Always Add Up


In the two years since we first covered the complicated rounding involved with soda bottle nutrition labels, some changes have been made with the goal of clearing up things like calorie count and serving size. But some questions still keep popping up, so it’s probably time for a refresher course.

In just the past few days, we’ve received a couple e-mails from readers who were a bit puzzled by what they read in the nutrition information for their carbonated beverages of choice.

First up is the reader whose daughter noticed that while both Diet Pepsi and Diet Sierra Mist had 35 mg of sodium listed on the label, they each had different percentages under the “% Daily Value” column.

So how could the same number, when divided by the same denominator, result in a different percentage?

Welcome to the world of FDA rounding rules.

According to those rules, food products in this sodium range must be rounded to the nearest 5mg increment for sodium.

This means that the Diet Pepsi could have as low as 32.5 mg while the Sierra Mist could
be as high as 37.4 mg, but both would say 35 mg on the label.

And when companies figure out what to put in the “% Daily Value” column, they use the actual, non-rounded number.

For sodium, the FDA uses 2400 mg as to calculate recommended daily values.

Say the Diet Pepsi actually has 33 mg of sodium, which comes out to around 1.375% DV, rounded down to 1% for the label.

And if Sierra Mist has 37 mg of sodium, that would come out to 1.54% DV, rounded UP to 2% on the can.

Meanwhile, another reader wrote in curious about the math on his 20 oz. bottle of Dr. Pepper Ten, which advertises “10 Bold Tasting Calories Per 8 Fl. Oz.” on the front of the bottle. But then both the nutrition label and the new-ish “calories per bottle” burst on the bottle only list 20 calories for 20 ounces.

Obviously, it Dr. Pepper Ten were actually 10 calories/8 oz, that number should be 25 calories.

Once again, it’s those tricky rounding rules.

Back when we first wrote about rounding rules, companies still divided up 20 oz. bottles into 8 oz. servings, so you ended up with 2.5 servings even though it’s intended and marketed as a single serving.

That has since changed, with nutrition info for all sodas 20 oz. and smaller listed as “one serving.”

But the issue here is that Dr. Pepper Ten apparently has fewer than 10 calories per 8 oz. As long as that number is 7.5 or higher, it’s rounded up to 10 — and “Dr. Pepper 8.235” is nowhere near as catchy.

Again, the actual, non-rounded calorie count is used to figure out the total for the bottle. So assuming Dr. Pepper Ten actually has 8.75 calories per 8 oz, you end up with 21.875 calories in a 20 oz. bottle. That is then rounded down to 20 calories.

Hopefully this will help to clear up why looking at nutrition labels can sometimes make you wonder whether or not you’ve lost your basic math skills.


Edit Your Comment

  1. Blueskylaw says:

    Thank you for the information on this, i’ve been wondering about this myself. With modern technology and in-line beverage analyzers, why can’t the exact number be listed? The machines used are very precise and the only thing I can think of is the companies will complain that it will cost them money.

    • Loias supports harsher punishments against corporations says:

      Part of it that they don’t have to have exactly the same size or nutritional content item to item; there is an allowed variance. So if something says contains 1000g of food, it could be anywhere from 995g and 1005g, as an example. So they round that, too, because labeling the exact nutritional content and size of every item, with their small variances, would be too cumbersome. So they round.

      • Firethorn says:

        While true for something like a frozen fried chicken dinner(size of breast/leg varies), for modern sodas it should be controlled to well under a percent for canned/bottled varieties. I know that fountains can be adjusted, and often are – the fountain for serving the drivethrough may well be set ‘richer’ to account for ice melt compared to the one out front for the inside customers.

  2. daynight says:

    The exact numbers should be used, accurate to the number of decimal places displayed. No reason not to. If there is something that is highly variable according to the source, then there should be simple and clear rules to make to as close as possible to the real value. This is the type of thing that should be a no-brainer to get correct.

    • Tunnen says:

      Maybe the current accuracy is 5 mg, if you really want to show it as a decimal you could list the rounding accuracy as 0.005 g.

      Or it’s just a carry over the older days where the testing was less accurate and they just haven’t revised the rounding rules now that the accuracy rate has improved.

  3. CrazyEyed says:

    I’ve noticed newer bottles of pop/soda have the exact number of calories listed on the side of the label. So why are some companies making us use algebra to figure out what we are eating or drinking?

    Its clear, they don’t want us to know (easily) how unhealthy the item is or how tiny the portion size really is.

    Anything seems healthy at 100 calories but once you check out serving size and servings per container it paints a completely different picture.

    The rounding one way but not the other is a bit rediculous as well.

  4. Such an Interesting Monster says:

    Y’know, you’d think they would require them to put the exact number with 1 decimal place. I mean, is it really that difficult?

    Sometimes I really can’t help but wonder how any of these agencies manage to function at all.

    • aerodawg says:

      They don’t require it because like any other mass produced item, there’s variances in the process. What’s listed on the label is a typical content plus or minus some margin of error. The typical margin of error is probably what the rounding rules are based on….

  5. RandomLetters says:

    Also remember that there’s an allowable 20% margin of error in there. 100 calories could really be 80 or 120 (I’m betting on 120).

  6. Browsing says:

    Why can’t they do everything per 100 grams, like they do in Europe, doesnt matter what I’m comparing, if it’s washing detergent or soda, manufacturing packing doesn’t count and the shelf label makes it all make sense….

  7. smo0 says:

    How about, “all this shit is bad for you, don’t drink it at all.”

  8. coldwatersrundeep says:

    Drink Diet Water, or just water. It’s a lot better for you.

  9. iesika says:

    Does that also explain how 0g of carbs can be 9% of my daily recommended?

    • perruptor says:

      Obviously, they’re using the “partial zero” developed by the California Air Resources Board for designating almost-clean cars. This groundbreaking mathematical concept is of enormous utility in all sorts of areas. I try and use it whenever possible.

  10. Invader Zim says:

    How, is a 12oz can of Diet Mountain dew 0 calories but a 20oz bottle of Mountain Dew has ten. What kind of rounding is that?

    • Coles_Law says:

      Say the 12 oz can has 4 calories-that rounds to 0.
      Then, 20 oz. has a bit over 6 calories-that rounds to 10.

    • bhr says:

      You will notice that with foods like pickles, gum, or crystal light packs too. If the serving size is smaller it will be 0 calories, but if the serving size is larger it jumps to 10.

      I don’t really have a problem with this, It makes the math easier for people counting cals to have everything rounded to the nearest 10. Even if you eat 20-30 individual items (ingredients, snacks, servings) a day that still only 40-120 extra calories, a negligible amount.

  11. NotEd says:

    What good timing!
    I’d just noticed the 20oz bottle of Diet Mt Dew I had with lunch today that says “10 Calories per Bottle” on the front and in the nutrition stats on the rear for “per Bottle”. The 8oz nutrition statistics list zero calories per 8oz serving.
    This confused me a littl a few hours ago, but I figured some mysterious rules for rounding were responsible.

  12. spartan says:

    I guess this explains how Bloomberg will let people buy 2 16 ounce colas, but not a single 32 oz cup.

    Think of all the calories that can be rounded out of ones diet.

  13. xanadustc says:

    Great job! Now, how does NYC round carbonated soft drinks?
    0-5 oz = Fun Size….
    5.1-10 oz = OMG that is a lot!
    10.1+ = YOU’RE GONNA DIE!!!!!

  14. HomerSimpson says:

    At least they all admit the serving size is 1 container nowadays (remember when there were 2 “servings” in a can?)

  15. dush says:

    The numbers are rounded and so are our bellies after consuming it.

  16. duncanblackthorne says:

    Why the hell round anything at all? How about accurate values, damnit! Some of us keep track of calories and grams of macronutrients for everything we eat every day, and it drives me nuts when everything fails to add up consistently because of this retarded rounding-up crap!

  17. yossi says:

    I import some candy from Israel. The calorie, fat and sugar count in grams has decimal points. The fruit snack I am eating now has 128.7 kcal, 2.7 g of fat and 14.8 g of sugar. AND it breaks down the sugar into 10.1 g of natural sugar (from the fruit) and 4.7 g of added sugar I LOVE IT!

  18. Awesome McAwesomeness says:

    This stuff is so confusing. I recently came upon a pizza that was labeled as being for one with two servings listed on the label.

  19. bwcbwc says:

    They really should round to the full resolution of the least significant digit or 1 mg. Or 1/20th of a serving size, whichever is smaller. I’m always annoyed by how coffee creamer with its partially hydrogenated oils is always able to label with 0% transfat even though it’s in the ingredients.