How many pieces of curved track do I need to make a circle?

As we all know it takes 360 degrees to create a circle, a standard curve is 22.5 degrees and a double curve is 45 degrees.

So to create a circle using double curves you would need eight pieces of track, and to create a circle using standard curves you will need twice as many as it is half the angle, which makes sixteen pieces of track.

The number is not dependent on the radius.

For convenience, Peco makes packs of track in OO and N gauge which come in half circles.

In summary:

Standard curves: 16 pieces to a circle.

Double curves: 8 pieces to a circle.