A radius reaches from the centre to the circle. With radius 3 m, the diameter would be 6 m; entering 6 as the radius would make the area four times too large because radius is squared.
Keep the exact result as 9π m²
A = πr² = π × 3² = 9π m². The integer coefficient 9 is exact and remains attached to the symbol π.
The decimal approximation is about 28.2743338823 m²
Multiplying 9 by the runtime approximation of π gives a finite display value. That number is useful for scale, but it is marked approximate and never replaces 9π in AreaCalc's exact conversion path.
Check radius versus diameter before calculating
If the measured 3 m were actually the diameter, the radius would be 1.5 m and the exact area 2.25π m² — one quarter of 9π. The calculator deliberately asks for radius and does not guess which measurement you supplied.