I've found myself rushing to the store when I run out of laundry detergent, pausing in front of the display for a moment.

There are small and large bottles side by side, and just looking at the price tags, the larger one seems overwhelmingly expensive.

However, when you calculate the cost per load, the story changes completely.

A 92-ounce bottle of Tide costs about 18.7 cents per load based on 64 loads.

The smaller 50-ounce bottle of the same brand costs about 28 cents per load based on 32 loads.

The bottle size is not even double, yet the cost per load is nearly a 33 percent difference.

It's not just a feeling of "the bigger must be better"; the numbers confirm the difference, which surprised me a bit.

There's a reason why the advice is to look at the price per ounce, not just the total price when choosing detergent.

These days, many stores have the price per ounce printed in small text below the price tag, so with just a quick calculation on your smartphone, you can easily compare.

In fact, consumer media research shows that Tide liquid detergent at Costco and Sam's Club is the cheapest at 12 cents per ounce among stores.

Going with no-name brands, BJ's and Sam's Club drop to as low as 8 cents per ounce.

Interestingly, the price per load varies significantly not only by brand but also by the type of detergent.

Bulk liquid detergents with over 100 loads cost between 8 cents and 11 cents per load. In contrast, capsule detergents, commonly known as pods, range from 25 cents to 45 cents per load.

Seeing the numbers makes it clear that the convenience of just dropping in one pod without measuring comes at a higher price than expected.

Costco's private label, Kirkland laundry pods, is also worth comparing.

A pack of 152 pods costs about 13 to 15 cents per load, while Tide pods, which are the same type, cost around 25 cents per load—almost double.

Whether you switch brands or not, choosing a larger size solves half of the savings issue.

I'm curious about how much this difference would add up over a year. According to Energy Star, the average American household does about 300 loads of laundry a year.

If you multiply the earlier mentioned difference of 9.3 cents per load between the small and large bottles by 300 loads, it amounts to about $28 a year.

If you switch from pods to bulk liquid, the calculation gets a bit bigger.

Multiplying the difference of about 25 cents per load for pods and around 10 cents for bulk liquid by 300 loads results in savings of about $45 a year.

While switching one detergent may not seem like a huge expense, considering that it can save you the equivalent of about ten cups of coffee each year, it's not an insignificant amount.

When using warehouse stores like Costco or Sam's Club that have membership fees, it's wise to factor in those costs as well.

If you're not just buying laundry detergent but also purchasing other household essentials in bulk, the membership fee can be quickly recouped. Conversely, if you're only going to a warehouse store for detergent, you should check the actual savings after deducting the membership fee.

Using Amazon's subscription option for bulk purchases can eliminate the need to go out each time, and often comes with additional discounts, making it a viable option for households that find store visits cumbersome.

Of course, bulk isn't always the right answer. If you don't have enough space to store detergent, one large bottle could become a burden.

There's also talk that opened liquid detergent can lose its cleaning power over time, so for households that do less laundry, there's no need to rush into buying the largest size first.

The next time you run out of detergent, I recommend checking the unit price printed in small text below the price tag.