The names on a fragrance bottle describe concentration, not quality or scent family. The scale is real but looser than the confident terminology implies.
What the concentration measures
A fragrance is aromatic compounds dissolved in alcohol with a small amount of water. The concentration figure is the proportion of that aromatic material in the finished liquid.
Higher concentration means more scent molecules per spray, which generally produces stronger projection early on and a longer period before the scent disappears.
The traditional ladder runs from cologne through eau de toilette and eau de parfum to extrait, with each step carrying a higher proportion of aromatic material.
The categories overlap in practice
These names are conventions rather than legally defined thresholds in most markets, so a house can label a product where it chooses.
One brand's eau de toilette may contain more aromatic material than another's eau de parfum, and both descriptions can be entirely accurate within the convention.
The practical consequence is that concentration names allow comparison within a single house far more reliably than across different houses.
Concentration is not the same as intensity
A perfume built mainly from heavy base materials can smell powerful at a low concentration, while one built from light citrus can smell restrained at a high one.
Some materials are perceptible at extremely low levels and dominate a composition regardless of how much of everything else is present.
Perceived strength therefore depends on which materials were chosen at least as much as on how much total material was dissolved.
Versions are often reformulated rather than diluted
An eau de parfum is rarely a stronger dilution of the matching eau de toilette. The two are usually built separately with different proportions.
Because heavier materials survive longer, the more concentrated version tends to lean warmer and deeper, while the lighter version emphasises the fresher opening.
This is why people frequently prefer one version over the other rather than simply choosing between weak and strong.
What this means for choosing between them
A higher concentration is not automatically better value, since fewer sprays may be needed but the price per volume is also higher.
Climate matters, because heat accelerates evaporation and can make a concentrated fragrance overwhelming in the same way it makes a light one disappear.
Testing both versions on skin over several hours is the only reliable comparison, since the names describe quantity rather than the experience of wearing them.