The fretless banjo requires the player to find notes on the fingerboard without the use of frets. Many fretless banjos have position markers inlaid into the fingerboard to help with way finding. But not all do. There are a few bits of knowledge about the construction of the banjo that can be helpful in getting started with fretless and finding notes.
Scale Length
The scale length of a stringed instrument refers to the length of the string from the nut to the bridge saddle. See the BanjoCraft Scale Length article for more detail on this. The scale length determines the spacing between each fret on the fingerboard. Even though the fretless banjo does not have frets, it can be helpful to imagine that frets are there. It may even be worth marking fret positions on the fingerboard with some low-tack tape.
How to Find Scale Length and Fret Positions
Use a tape measure or long ruler to measure the distance from the nut to bridge saddle. Then, pop over to the StewMac fret position calculator. Use those measure measurements to place tape on the fingerboard at the appropriate places.
The Fretless Banjo Bridge is Movable
While the builder of a fretless banjo may have a had a specific scale length in mind during the build process, the player can move the bridge around to suit their own tastes. A player might move a bridge to get a different sound from the head or to make the note spacing more comfortable for their reach. Doing this on a fretted banjo would result in the instrument playing out of tune, because the frets would still be spaced to work with a specific bridge placement. However, since the fretless banjo does not have frets, the bridge can be moved closer to or further from the nut. Just keep in mind that moving the bridge changes the scale length and the spacing of notes on the fingerboard.