The size of caster cups you should get is determined by the type of caster (wheel) on your piano. If you have the smaller, single wheel type caster, then get the smaller caster cups. Likewise, if you have the larger, double-wheel casters, then get the larger caster cups. The measurements (diameter) of the different caster cups are provided on each page.

Unfortunately, there is no database that tells you what size your casters are, based on either make or model, so you are going to have to measure yourself. When measuring, you want to measure the width of the wheel (for people with double wheels for example, the length usually is not the issue, but the width of having two wheels next to each other can make them too wide to fit a smaller caster cup). Think of it like measuring the tread on your tires.

Something to consider for larger pianos (approximately 5'8 or above):

A piece of advice we often give, is if you have a larger piano, even if your wheels will fit in the smaller 3-1/2" caster cups, you may still want to consider getting the larger 5" caster cups. The reason for this is proportion. A large piano on smaller caster cups can at times make the piano look disproportional.

Imformative Links:

Why do you need piano caster cups?

How to decide what size caster cup to get

How to install piano caster cups yourself (without professional movers)

Satin vs. high polish caster cups