Is the family size pack really cheaper? Not always

I have a cupboard that I call "the museum". It contains a 1 kg bag of coffee I bought because it was the sensible, grown-up, cheaper-per-gram choice. The last third of it tasted like cardboard that had been told about coffee once.

So, is buying in bulk cheaper? Usually yes on the shelf label, and often no in real life. The big pack only wins if you actually use what's inside before it goes stale, soggy or forgotten. And sometimes it doesn't even win on the shelf label. I built Price Per Everything to stop arguing with myself in the supermarket aisle, and here is what it told me.

The coffee bag that stops being a bargain

The tool ships with a coffee example: a 250 g bag for 4.99 € and a 1 kg bag for 15.49 €. If you use every single gram, it's not even close:

• 250 g bag: 19.96 € per kg
• 1 kg bag: 15.49 € per kg, so 22.4% cheaper

That's the number the big bag is proud of. But the example also has a Waste % field, and that's where it gets interesting. I played with it for the 1 kg bag:

The break-even sits between 22% and 23% waste. In plain words: if you throw away (or grimly drink) more than about a fifth of the big bag, the small bag was the better deal. My museum bag was well past that line.

The same thing happens with fresh food, only faster. I compared a 4 × 150 g yogurt multipack for 1.79 € with a 1 kg tub for 2.19 €. Without waste, the tub is 27% cheaper (2.19 € vs 2.98 € per kg). But if 40% of the tub ends up at the back of the fridge growing a personality, the tub costs 3.65 € per kg and the little cups are 18% cheaper. Small portions have one superpower: you can't half-finish a cup that's already finished.

When "family size" is simply more expensive

Here's the part that surprised me most, because it has nothing to do with waste. Supermarkets know we've learned that "bigger = cheaper per gram", and they don't always play along.

I typed in three cereal prices of the kind I see all the time (my own example numbers, not a specific shop):

The family pack is the most expensive option per gram, even with zero waste. The normal small box is 5.9% cheaper, and the small box on sale is about 25% cheaper than the "family" one. Two small boxes on sale give you exactly the same 750 g for 3.98 € instead of 5.29 €.

This happens more than you'd think, especially when the small pack is on promotion and the big one isn't. The shelf label usually shows a price per kg, but it's tiny, sometimes uses different units (per 100 g here, per kg there), and nobody reads it while a child is negotiating for sweets.

How I use the tool in 30 seconds

You don't need to do anything clever:

1. Compare by: "Quantity unit" for groceries. Use "Use / wear" for shoes and clothes, "Serving" for things like protein powder, "Hour of use" for gadgets, "Year of lifetime" for appliances.
2. Products: one row per option. Enter the price and the quantity in the same unit for every row: 250 and 1000 for grams, not 250 and 1. Put "g" or "ml" in the unit label so you notice if you mixed them up (the tool warns you when the labels differ).
3. Waste %: be honest. How much of the big pack did you throw away last time? If you don't know, try 0, 10 and 25 and see whether the winner changes. If it changes at 10%, the "saving" is fragile.
4. Read the × cheapest column. 1.05× means "basically the same, buy what's convenient". 1.3× means one of them is quietly robbing you.

The same idea works outside the kitchen. The shoe example in the tool compares 40 $ budget sneakers that last 120 wears with 180 $ leather boots that last 900: 0.33 $ vs 0.20 $ per wear, so the expensive boots are 40% cheaper per use. Bulk buying in reverse: paying more up front wins when you actually get the use out of it.

Be honest: what the tool doesn't know

I'd love to say the tool solves grocery shopping. It doesn't. A few things it can't see:

• Your waste. The Waste % field is only as good as your guess. The tool doesn't know your fridge, your kids or how fast coffee goes stale in your kitchen.
• Quality. It compares price per gram, not taste. If the big bag is a cheaper bean, that's on you.
• Money and space. Bulk ties up cash and cupboard space. The tool doesn't put a price on a cupboard that won't close.
• Currencies and taxes. It doesn't convert anything. Enter all prices in the same currency, including the same taxes and shipping.
• Your time. Two trips for two small boxes may cost more in petrol and patience than the 1.31 € you saved.

What it does well is the one thing my brain does badly at a shelf: turning "4.99 € for 250 g vs 15.49 € for 1 kg, but I'll probably waste some" into one clear number.

The short version

• Bigger packs are usually cheaper per gram, but not always. Check, especially when the small pack is on sale.
• Waste eats bulk savings fast. For the coffee example, about 22% waste wipes out the whole advantage.
• For fresh food, buy the size you will finish, not the size that looks smart.

Try it yourself with the coffee example on Price Per Everything: click "Coffee: small vs. large bag", then change the Waste % of the 1 kg bag to 25 and watch the winner flip. And if you have a museum cupboard of your own, I'd like to hear what's in it.