How many reeds does a room need?
A reed diffuser works against the volume of air in a room rather than its floor area, so a tall room needs more sticks than a low one of the same footprint. Enter the width, length and ceiling height with the coverage figure printed on the product, and the stick count follows; add the replacement interval and the unit price and the yearly usage and cost follow from there.
The maths is a volume division. Room volume multiplies width by length by height, and the stick count divides that by the volume one stick covers, rounded up. Replacements per year divide a 365-day year by the interval, and the yearly stick usage multiplies the stick count by that figure, rounding up only once at the end.
No official source publishes a stick count per unit of room volume, because throw strength differs by product, so the coverage figure is yours to enter from the label. If the label has none, borrow the figure from a product of the same bottle size. Judging scent strength, predicting how long a bottle throws and the effect of ventilation or air conditioning are not covered.
Frequently Asked Questions
Borrow the figure from a product of the same bottle size. No official standard exists for sticks per unit of room volume, so the label is the only basis.
Use the service life printed on the product or the interval you have found in practice. Changing it shows how the yearly cost moves.
Scent strength is not judged here. The count comes only from the coverage figure, so adjust by how the room actually smells.