How many square inches are in 64 square millimeters?

Answer 1

There can be no conversion.

64 mm squared is a measure of area in 2 dimensional space whereas an inch is a measure of distance in 1 dimensional space. The two measure different things and, according to the most basic rules of dimensional analysis, conversion from one to the other is not valid.

Answer 2

25.4 mm = 1 in

→ 25.4mm × 25.4mm = 1 in × 1 in

→ 645.16 mm² = 1 in²

→ 64 mm² = 64 ÷ 645.16 in² ≈ 0.10 in²