The cream from the site mentioned is ALREADY whipped, hence only 8.6g / 15mL, due to air entrainment. Heavy cream is very close to the same density as water or 1g / mL. So, your 6g fat in 15ml (15g) of cream is about 40% fat. Given that there is only one significant digit on these nutrition labels, your true value could range from 5.5 to 6.4 grams of fat or about 36% – 46%. If you truly had 6g of fat per 8.6g cream, you’d be looking at a whopping (not whipping) 70% fat content!

Here’s a way to think of it:
calcium is bound to numerous proteins (caseins) that are specifically removed to make heavy cream. With those proteins removed we are indeed left with our heavy cream product that is virtually void of calcium.

It is kind of funny though as we have dairy and calcium so linked in our brains.

–McAuliflower

I’m not sure and haven’t done the sleuthing yet, but I would immediately suspect that the 2% milk you see is measured as a percentage of mass (or weight). Of course most of the mass of milk is simply water.

FYI “Whole milk” on the shelf contains about 3.25% fat. While it is not an uncommon misconception in the public, 2% milk doesn’t contain 1/50th of the fat of whole milk.

While my thoughts on the ethics of the dairy industry’s marketing teams are none too flattering, I don’t think these percentages were devised to deceive. They provide us valuable metrics by which to plan our homemade ice cream adventures!

The idea that 2% milk used to qualify as ‘low fat’ on the other hand. That is just plain deceptive.

You can probably consider your milk or cream to be homogenous.

By contrast, if you try to pour 50 grams of table sugar into ice cold tea you will notice it doesn’t all disolve. Because it doesn’t disolve, you expect the stuff at the bottom of the glass to be sweeter after you stop stiring. This illustrates the idea that that iced tea is not homogenous. If it was, the sweetness would be the same in any sip (sample) you took.

Our store-bought milk and cream doesn’t behave that way. If you were to take fresh milk and let it sit, you would notice after a while that the milkfat would begin to separate and float. If your milk did that then you could not consider it homogenous and proportions wouldn’t provide an accurate way to blend to the fat percentage you seek.

checking your math:
equal parts 10% and 18% will give you 14%
(1/2 of total measure * 10%) + (1/2 of total measure * 18%) or
(10 * 1/2) + (18 * 1/2) =
10/2 + 18/2 =
5 + 9 =
14%

and two parts 2% and one part 35%
(2/3 of total measure * 2%) + (1/3 of total measure * 35%) or
(2/3 * 2) + (1/3 * 35) =
4/3 + 35/3 =
39/3 =
13%

I was hoping you might be able to provide some insight on how I compensate when I’m unable to find the percentage I need. When I make ice cream, I try to end up with approximately 12-15 percent fat. What I usually do, then, is mix equal parts 10 and 18 percent or two parts 2 and one part 35 percent. I’ve always wondered whether this is a legitimate way to achieve the fat percentage I’m looking for, or whether I’ve missed something crucial. Any thoughts?

The International Dairy Foods Association defines away the ambiguity.

Light Whipping Cream:

contains not less than 30 percent milkfat, but less than 36 percent milkfat. Light whipping cream may also be called “whipping cream.”

Heavy Cream:

contains not less than 36 percent milkfat. Heavy cream may also be called “heavy whipping cream.”

Ack!
Is that by weight or by volume? They didn’t say! I’m sure that what is in the fridge right now is 36% or greater based on both the USDA and the IDFA, but I feel the call of science (or is that the Wolaver’s IPA?).

Because math is fun, we will figure out what we have…

Google books gives us our first clue:
Dairy Chemistry and Biochemistry – by P… L… H… Mac Sweeney, Patrick F. Fox, …

Milk fat has a density of about 902kg m^-3 at 40° C

Some unit conversion and we see milkfat has an approximate density of 900 grams per 1000 milliliters (1000 liters = 1 cubic meter).

The pint in the fridge claims 6 grams of total fat per serving. A serving is 15 milliliters. So we have matched the units.

The next step is to either

1. scale 900g/1000mL down to the grams of total fat per serving so we can compare the volume of pure milk fat to our serving size. That will give us fat by volume or
2. scale 900g/1000mL down to the serving size so we can compare the mass of pure milk fat to our total fat per serving. That will give us fat by mass (which is the same as fat by weight when measured in our kitchen).

   By volume, I see 45% milkfat, and by weight I see 41% milkfat. Huh? That is well in excess of 36%. Those numbers are very rough because we are working with several measures of low or unknown precision.

   And something else. McAuliflower noticed that our “Heavy Whipping Cream” has no appreciable calcium. Apparently, the calcium is bound to the protein and other milk solids which are not milkfat (those other solids make up some 9% of whole milk).

   Oh well, at least Heavy cream is low on sodium and has a low glycemic load!

   Oh, and the handy unit calculator at the bottom of that page says that 15ml (approx 1 tbsp) of Heavy Cream is 8.6g. If our cream has 6g of fats alone, that would tend to support the theory that our cream is heavier than heavy.