An implant's diameter/projection varies proportionally (not directly) as its volume. Meaning (for example), a 200cc implant may be twice the volume of a 100cc implant, but a 200cc implant doesn't have twice the diameter/projection of a 100cc implant.

The following chart should help illustrate the relationship of volume to diameter (and thus projection, where diameter is twice the size of radius, and projection having the same value of radius). For want of a better way of calculating this, this chart assumes a perfect half-sphere.