Span
Span means how far something can extend end to end. My bar compass can span 20cm. Some synonyms are reach, stretch, spread, and distance.
This bar compass can span a distance of 30cm. Here it is set at 20cm. We can create an arc equal to 20cm. We can also create a circle with a radius of 20cm. That circle will have a diameter 40cm. It will have a circumferance of 125.6 cm.