Fence quotes and maker projects often need the distance around a round edge, not the floor space inside. A table skirt follows the rim. A jogger track lane is a circumference problem before it is an area problem. Enter radius; read the distance around.
Area and circumference share radius but answer different questions. Mixing them is the common mistake—inside versus around.
Circumference with radius 6 matches the default—still checked against 2πr on a napkin.
Around the edge, not across the room
Diameter times π is circumference; diameter squared times π is not. If someone gave you a diameter of 10, radius is 5 before you paste. For the space inside the same circle, area with radius 6 is the paired check.
Straight-edged layouts use different forms—perimeter of a 12 by 9 rectangle. Metric rim measurements sometimes need 2 meters in feet before you order stock by the foot.
- One radius field—convert diameter first.
- Result is a length, not square units.
- Copy radius beside the circumference in notes.
Ordinary shop and class geometry, not precision manufacturing tolerances.