The forty-eight rolls were a bargain. The rest of the cart wasn't.

The question

Is the warehouse club membership worth it, and is that forty-eight-roll tower of paper towels the proof?

My wife wrote a list. I brought it with me. Both of those things are true, and only one of them turned out to matter.

The Dad Math

This was done in the parking lot, leaning on a flatbed cart, with the confidence of a man who'd just eaten four free samples of teriyaki jerky.

Every number in this column is an example. Swap in your own.

• Membership: $60 a year
• Club paper towels: 48 rolls for $48, so $1 a roll
• Grocery store paper towels: $1.75 a roll
• Savings: 75 cents × 48 rolls = $36, on paper towels alone
• "And we buy other stuff too, so the membership paid for itself before we hit the registers."
• Conclusion: they're basically paying us to shop here.

Clean. Fast. Wrong in about five places.

The real math

Step 1: A roll isn't a unit

Rolls come in big, mega, double, triple and whatever word marketing invents after "triple." Counting rolls is like comparing trucks by how many doors they have.

Compare price per sheet or per square foot. Most shelf tags print that in small type under the big price. Check that both tags use the same unit, because one store will say "per 100 sheets" and the other "per square foot," and suddenly you're doing algebra in aisle nine.

Example: the club roll has 100 sheets, the grocery roll has 150.

• Club: 48 rolls × 100 sheets = 4,800 sheets for $48. That's $1.00 per 100 sheets.
• Grocery: $1.75 ÷ 150 sheets = about $1.17 per 100 sheets.
• Getting 4,800 sheets at the grocery store takes 32 rolls: 32 × $1.75 = $56.
• Real paper towel savings: $56 − $48 = $8.

Not $36. Eight. Same paper towels, same Saturday, twenty-eight fewer dollars of bragging rights.

Step 2: The rest of the cart, which is where the club earns its keep

The club really can save you money on things you'd buy anyway. Example: $200 of routine stuff like coffee, dish soap and dog food, at 15 percent less than you'd pay elsewhere. That's $30.

Real savings so far: $8 + $30 = $38.

Hang onto the phrase "things you'd buy anyway." It's doing all the heavy lifting in this column.

Step 3: The membership's share

$60 a year ÷ 6 trips a year = $10 per trip.

Step 4: The drive and the time

The club is a 24-mile round trip. The grocery store is 4. The extra 20 miles at an example 30 cents a mile for gas and wear comes to $6.

Time: the club run takes an hour and a half once you count parking in a different zip code, the checkout line, the receipt check at the door and the kids' full lap of the sample stations. The grocery run takes 45 minutes. The extra 45 minutes at an example $20 an hour is $15.

You'll feel tempted to count your Saturday as free. Your Saturday doesn't feel free when it's gone.

Step 5: The hall closet's rent

Forty-eight rolls claim about 3 square feet of closet floor or a full garage shelf. Say a storage unit near you charges $100 a month for 100 square feet (an example). That's a dollar per square foot per month. If your household finishes the stack in about six months, that's 3 × 6 = $18.

If that space was truly empty, count zero. If the paper towels push the camping gear into the garage, and the camping gear pushes the car into the driveway, count all of it. Why your garage filled up, and how to get it back is about exactly that chain reaction.

There's a quieter cost too. With forty-eight rolls in the house, nobody rations. Paper towels become napkins, dust rags, coasters and one child's volcano cleanup.

Step 6: "While we're here"

These are the three most expensive words in retail. Mine were a three-pound tub of spinach, two-thirds of which became compost by Thursday, a jumbo pack of batteries for devices we don't own, and a tub of cheese puffs roughly the size of a toddler. Call it an example $40 of things that weren't on the list and wouldn't have been bought anywhere else.

That isn't savings. That's spending in a bigger building.

(There was also a kayak. My wife talked me out of it in aisle twelve, which is the single best financial decision in this column.)

The tally

• Savings: $8 + $30 = $38
• Costs: $10 membership + $6 miles + $15 time + $18 storage + $40 impulse = $89
• Net: −$51

"They're basically paying us to shop here" meant paying fifty-one dollars to shop there.

The same trip, run by the person who wrote the list

She stops at the club on the way home from somewhere she was already going, so the extra time is close to zero. The extra miles still cost $6. The cart is $300 of routine items and nothing else. The paper towels go on a top shelf that was actually empty.

• Savings: $8 + $45 (15 percent of $300) = $53
• Costs: $10 + $6 = $16
• Net: +$37 a trip, or $222 over six trips a year

Same store, same membership, same tower of paper towels. One of us had a list. The other had a flatbed and a dream.

A real safety note, no joke attached. If your bulk stash lives on garage shelving, anchor the unit to the wall studs. How to hang heavy things so they never come down covers the hardware. Keep heavy cases of water, liquids and pet food at waist height or lower, and put light stuff like paper towels up top. Reach high shelves with a step stool or a ladder, never a chair, a bucket or the cart.

The verdict

The membership pays off when your yearly membership fee ÷ your real discount is less than what you'd spend there each year on routine stuff. At the example numbers, $60 ÷ 0.15 = $400 a year of things you'd buy anyway. To find your actual discount, price ten of your regular items at both stores once, per unit. It takes twenty minutes and settles the argument for good.

Each trip pays off when the routine savings beat the extra miles and time. In the example, the extra trip costs $21, so you need at least $140 of list items (that's $21 ÷ 0.15) just to break even.

Count everything not on the list against the trip, in full.

Compare per sheet, per ounce or per load. Never per roll, per bag or per "value pack."

And only buy in bulk what won't spoil and already has a home. Paper towels pass. Spinach doesn't.

Run your own numbers in the BRO cost-per-use calculator before the renewal notice shows up.

Next trip, my wife's pushing the flatbed. I've been put in charge of holding the list, which I'm told is a promotion.