Area of a Circle

The area of a circle is π times the radius squared: A = πr².

Radius, not diameter

Circumference uses the diameter. Area uses the radius. Mixing them is the usual slip.

The units tell them apart

Circumference is a length in cm. Area is a coverage in cm². Check the units of the question.

Square first

In πr², the radius is squared before multiplying by π. Order of operations, as always.

A different question, different units

Area = π × radius². Circumference is a length in centimetres; area is a surface in square centimetres. The two formulas look similar and answer completely different questions, so read carefully which one is wanted.

The radius, not the diameter

The area formula uses the radius. Substituting the diameter gives an answer four times too big, since the radius is halved and the halving is then squared. If a problem gives the diameter, halve it before doing anything else.

Square first, then multiply by π

For a radius of 3, the area is π × 9 ≈ 28.3, not (π × 3)² . Order of operations puts the exponent before the multiplication. Writing πr² with the square attached only to the r is the notation reminding you of this.

Exact answers keep the π

An area of 9π square centimetres is exact; 28.27 is rounded. Unless a problem asks for a decimal, leaving π in the answer is more precise and often expected. It also makes later calculations cleaner.