From paper to project
Draw a circle 20 cm in diameter.
Divide it in half and cut one semicircle.
Bring its straight edges together into a cone.
Allow a 1 cm overlap and tape the exterior join.
Try the gift, leaving roughly 2 cm free at the top.
Close with a tag or stand the cone in a stable holder.
Check it with an example
A semicircle with a 10 cm radius has an arc about 31.4 cm long. The cone’s rim is slightly smaller because of the overlap.
If it does not turn out as expected
Use a stand if it tips rather than loading it with extra weight. Retain original packaging where contents need protection.