Pi is irrational: its decimal expansion never terminates or repeats. Keeping a rational coefficient beside π preserves the mathematical value; evaluating that expression produces a finite approximation for practical display.
Radius 3 gives exactly 9π
The circle formula is A = πr². Substituting r = 3 gives π × 3² = 9π. No decimal digits of π are needed to establish that exact result.
Convert the coefficient before evaluating π
If the radius is 3 m, the exact area in square feet is the exact rational conversion of 9 m² multiplied by π. AreaCalc converts that coefficient first and leaves π symbolic, avoiding a rounded decimal from becoming the input to another conversion.
Use the decimal for scale, not as a new exact input
The approximation helps compare sizes and communicate a finite number. Its last shown digit is rounded. For chained exact work, retain the π expression; for physical projects, measurement uncertainty will often exceed the displayed numerical rounding.