Have you ever heard of the story about the M&M packaging size mysteryr? I heard this first on Planet Money Podcast but I thought it was a great story of marketing decision making.

It was noticed on a visit to a local convenience store that Peanut M&M and Regular Chocolate packages contained a different weight. What was intriguing was that the weight difference was only 0.06 ounces. Peanut Butter was 1.63 oz vs. Chocolate 1.69 oz.

There must be a reasonable explanation for this.

Theory #1 – Cost

The first thought that came to mind was this had to be because of profitability. PB packages weighed less because it cost more to produce. In order to keep margins the same, a different package size was filled for each. However,  this was proven incorrect because it was determined that chocolate was actually more expensive than Peanut Butter.

Theory #2 – Operational Constraints

How about theory #2. A machine drops the same amount of M&Ms in each bag and maybe PB weighs less than chocolate. So if each bag had the same candies, naturally PB will be less. This preciseness from the machine to put in the same amount of each product determined the weight in each bag, thus a discrepancy. But when the bags were opened up again, this theory was also debunked. In fact the PB pieces were slightly different sizes and weight so M&M had the flexibility and choice to decide any weight they wanted.

The True Reason – Health

So what was the reason? After contacting Mars to ask for a statement, the real reason came to light. Calories. M&M’s wanted to maintain the magical number of 250 calories or less on any snack item that they sold. They felt this was the magic number to entice customers that wanted to feel less guilty about consuming their products.

So there you have it. A packaging discrepancy decided by a consumer insight on the threshold of calories/portion one prefers to eat. Sneaky work Mars. I know its supposed to make me feel better but then again does it matter what the packaging says? I end up eating 3 of them in one sitting.