Dentists describe tooth colour with a shade guide: a set of tabs from lightest to darkest. On the VITA classical guide there are sixteen. A typical course of professional home whitening lightens teeth by two to four tabs.
Why the claims vary so much
Some products count “shades” on a guide reordered by colour rather than value, or count half-steps. A change of one tab can be anything from barely visible to obvious depending on which tabs they are — the colour difference (ΔE) between neighbouring tabs is not constant.
What affects your result
Yellow-brown teeth tend to whiten well; grey teeth less so. Fillings, crowns and bonding don’t change colour at all, which is why we check for them first.
You can try it on our home page: pick your shade and move the slider to see the change and the colour difference in numbers.