It is a truism that Costco is cheapest. Large packages of deeply discounted household items are your hard-earned prize when you shlep there, box your own booty and lug said haul to your car. But what if we’ve all been using the bulk buying truism as an excuse to stop doing our homework? Yes, you can save money, but at the end of the day it always comes back to the per unit price. Herewith, how to get bang for your bulk:

1.  PER UNIT PRICE. It’s the only measure of whether your deal is worth it. And while bulk outlets are generally competitive, they do not always offer the lowest cost per unit (CPU). Bar-code reader apps like Red Laser are not yet effective in Canada, but they’re on the way, meaning that you’ll imminently be able to point your phone at a bar code and instantly know if you’re getting the best CPU. In the interim, for basic items you should keep in mind what you generally pay per unit for the items you use.

2. STICK TO YOUR LIST. If you know that your local warehouse store’s diapers, olive oil and extra-strength pain reliever represent good value, go for these items, but don’t stray from your list without doing your legwork. It’s the chocolate that you throw in the cart at the last minute, not bothering to calculate that it’s cheaper to buy individually at your local, that throws off the savings.

3. CALCULATE THE COST OF YOUR BULK. Yes, you save on purchase, but what about the cost of storing all that meat you got in an extra deep freeze? That can run you  another hundred bucks a year. Now add in gas, time spent driving, breaking down boxes, membership costs and the spoilage factor if you buy fresh goods you don’t end up consuming, to determine if your efforts are yielding savings. For a certain brand of hummus cocktail (Yes, such a thing exists. Deliciously.), the sale price, consistently on offer at my local markets, is cheaper than Costco. I’d be foolish to buy it there (though I’d still be foolishly happy, because, as mentioned, it’s delicious).

4. THINK SMALL. At the opposite end of bulk is sample size, or to be more precise, the smaller quantities available at discount shops and dollar stores. A recent article in the Report on Business Magazine broke down cost per unit, and revealed, counterintuitively, that buying small at Dollarama is often the very cheapest way to go. The convenience of not having to warehouse it, however, may be mitigated by the amount of bottles you’ll have to buy of cheaper CPU dish soap to equal a giant tub of the stuff.

5. DON’T NEGLECT THE CLUB PACK. Grocery stores, eager to keep their discount customers from going to warehouses, have amped up their own bulk offerings. At larger supermarkets you’ll often find ‘club packs,’ an aisle or two of bulk durable goods that, with perpetual deals and discounts, often equal the price per unit of what you’ll find at a warehouse.

6. BULK V. BULK. The math gets tricky, but it’s worth it to do the calculations once to figure out where to buy your bulk staples. For example, though Costco quinoa is half the price of what I can find at the supermarket, it actually comes in around the same price as my local bulk grain shop. Translation – no more shlepping.

7. BEWARE BULK BRAIN. It’s important to strike a balance between being a hoarder and a saver. Beware the impulse to stock up on piles of space consuming stuff you will never ever use. Or worse, frivolous and unhealthy stuff you will consume out of guilt, and even grow accustomed to (I’m looking at you, extra large bags of pita crisps!)