Bulk buying is usually approached by picking a pack that looks about right. A short calculation produces a considerably better answer and takes under a minute.
The Three Numbers
How many people or items you are covering. How many pieces each one consumes. And how much spare margin you want.
Multiply the first two, add the margin, and compare that against the pack sizes available. That is the whole method.
Worked Through
A class of thirty, one item each, twenty-five per cent margin: thirty-eight. So a pack of forty rather than one of twenty-four.
A party of twenty guests, two napkins each, generous margin: sixty. A pack of a hundred covers it with leftovers for next time.
A clinic using two rolls a day, five days a week, ordering monthly: forty. Which is more than a twelve-pack and suggests ordering in multiples.
Catalogues that publish the count on every card and provide the arithmetic, of the kind at juvale.net, make this comparison possible without opening every listing.
How Much Margin
- Ten per cent: where you can reorder easily and running short is survivable
- Twenty-five per cent: the sensible default for most situations
- Fifty per cent: events, classrooms and anything where running out is visible
- More: only where the item keeps indefinitely and storage is free
Cost Per Piece Is Only Half the Answer
A larger pack almost always has a lower unit price, which makes the arithmetic look one-directional.
The other half is what proportion you will actually use. Two hundred sheets at four pence each is cheaper than fifty at nine pence, provided you use more than about ninety of them.
Below that threshold the smaller pack was cheaper in the only sense that matters.
Storage Is a Real Cost
Bulk packs occupy space, and in a small home or a shared office that space has value.
The question worth asking before ordering is where it will live. A hundred mailers in a cupboard is fine; a hundred mailers on a kitchen floor for eight months is not a saving.
Consumption Rate Beats Guessing
The most accurate figure comes from observation rather than estimation. Note when you open a pack and when you finish it.
Two cycles gives you a real consumption rate, and every future order becomes a calculation rather than a guess.
Round to the Reorder Interval
The practical target is a pack that lasts roughly as long as you want to go between orders.
For a household that is often a year. For a small seller it is a month. Matching the pack to the interval avoids both frequent reordering and long-term storage.
Write the Numbers Down
Most organisations buy the same things repeatedly. Recording the count and the interval once removes the calculation from every future order.
