is that girth is the distance measured around an object while diameter is (geometry) any straight line between two points on the circumference of a circle that passes through the centre/center of the circle.

Is circumference a girth?

As nouns the difference between circumference and girth

is that circumference is (geometry) the line that bounds a circle or other two-dimensional figure while girth is the distance measured around an object.

Is girth measured in diameter?

Remote girth measurements

Girth measurements may be taken remotely using photographic means or through the use of a telescopic reticle. In these cases the diameter as seen from the surveyor's position is actually measured and the girth is calculated by multiplying the diameter by π (pi).