The unit price, that “second number” on most grocery aisle labels, compares apples to apples, literally, by weight.

If two containers of peanuts are different sizes, the unit price will tell you the price per weight, or dollars per amount of food. You can be sure to spend less on food.

The unit price, usually listed in a smaller font, also shows that the same retail price buys a much larger load of peanuts than cashews. The cashew is a more expensive nut.beans label

If you read unit prices regularly, you’ll start to notice that larger containers of the same item tend to have a lower unit price, even if the retail price is higher. That’s called a deal.

This is all brilliant if you aspire to a certain poundage of food per day. Of course, to get enough (and not too much) food, you need to eat an appropriate amount of calories, not pounds. That’s why the Nutrition Facts label is based on a 2,000 calorie reference point, not some number of pounds.

(A diet guided by daily intake of food by mass might make sense for an animal without such diverse tastes as humans.)

How could this imperfect system be improved? I propose a unit price label based on calories per dollar.

This is not a technical gripe. If you’re trying to eat well on a budget, how many calories per dollar you buy is central. And it applies equally to all, regardless of your daily caloric needs, which can range widely depending on age, size, gender, activity level, and other factors.

For example, I recently bought a pound of sole, a white, light, flaky fish, that was on sale for $9.99/lb. Not bad, I thought. Definitely cheaper by weight than the other fresh fish.

What I didn’t notice until later is that sole, which packs 91 calories per 100 grams, is not as calorie-dense as wild salmon (142 calories per 100 grams). So I must buy and eat more sole to consume the same number of calories. Keep in mind that I’m trying to consume a proper amount of calories each day in order to maintain a healthy weight.

The sole on sale was a good deal, but maybe not such a steal as I thought. The salmon, for example, was $12/lb – two dollars more per pound. Pricier, right? But recall that salmon is much more dense in calories (and, not coincidentally, beneficial fatty acids). As it turns out, I bought 400 calories of sole for $10 when I could have bought 640 calories in a pound of salmon for $12.

What if I’m determined to spend no more than $10 on fresh fish? For $10, I’m limited to 0.83 pounds of salmon, which contains just over 530 calories, which is 25% more than what I carried home in $10 of sole.

If I don’t overeat, calorie-dense healthy food like salmon will help me stretch my food dollar.

We’re used to hearing about calorie density as a bad thing, as it is associated with nutrient-poor, artery-clogging fast food. Also, most Americans consume far more calories than they need, according to the USDA and a chorus of authoritative sources. Eating more calories is not the solution. For these reasons, it may seem counterintuitive to suggest that shoppers maximize calories for their buck.

On the other hand, isn’t a major criticism of our food system that a healthy diet is too expensive? In this environment, it is essential for people to understand how to buy enough calories for the fewest dollars.

If practiced within the basic guidelines of a healthy diet, which must include calorie-sparse vegetables and fruits, you can use this framework to spend less money on food overall, with an eye toward consuming enough, and not too many, calories. Whether you cruise the aisles at Whole Foods or Walmart, the same principle applies. More calories per dollar is a better deal. By keeping an eye on metrics like calories per dollar, consumers, if they wish, can make healthier choices at the lowest possible price.

While traditional unit price comparisons of dollars per mass can still play a useful role, especially when comparing peanuts to peanuts, the consumer can only compare between foods by considering calories per dollar. (Or dollars per calorie, but then the figures become very small. For example, the sole cost me about $0.03 per calorie.)

Though we won’t see these figures displayed on the aisles soon, it’s easy enough to calculate calories per dollar for labeled packaged foods:

  1. Multiply the calories per serving size times the number of servings to calculate the total calories.
  2. Divide total calories by the retail price.

You might not choose to buy the cheapest healthy option for any number of reasons, but this is a good way of knowing what the cheapest healthy option actually is.