About this gear ratio calculator
Gear ratio = driven teeth ÷ driving teeth. 36 ÷ 12 = 3:1, so the output turns three times slower and, ignoring friction, with three times the torque: 1,800 RPM becomes 600 RPM and 10 N·m becomes 30 N·m. A ratio below 1 is an overdrive: faster and weaker.