Round coverage shows up in pizza orders, sprinkler heads, and pipe cross-sections. You have the radius—or the diameter halved in your head—and need square units for tile, paint, or a homework row. Enter radius; the form returns area using the usual πr² habit built into the page.
Circumference is length around the edge; area is space inside. If you need the perimeter, use the circumference page. If the shape has corners, this is the wrong tool.
Area of a circle with radius 6 is the default—people still sketch π×36 quickly and compare.
Radius, diameter, and unit labels
Halving a diameter of 12 gives radius 6, not area 12. Labels on diagrams lie sometimes—confirm which arrow is radius before you type. Mixed units need conversion first—30 centimeters in inches—then area in the unit you care about.
Rectangular floors still happen on the same job—area for a 12 by 9 rectangle—and round coverage on a label may need square meters to square feet after you have the number.
- Radius, not diameter, goes in the field unless you already converted.
- Area units square the length unit—feet in gives square feet.
- π is handled in the page; you do not type it.
The circle area easy-check note and the broader area for home projects note help when a deck mixes shapes. Reference geometry, not survey legal area.