Square Millimeters to Ares: the quick answer
1 mm² = 1 × 10⁻⁸ a
1 square millimeter equals 1 × 10⁻⁸ ares
To convert square millimeters to ares, multiply the value by 1 × 10⁻⁸. To go the other way, multiply ares by 100,000,000 to get square millimeters.