The Total length of a wire in a transformer is determined by multiplying the number of turns of a coil with the perimeter of the bobbin. Use the below total length of a wire formula to determine the heat losses you get in a transformer. The length of wire definitely has an effect on current and voltage. Resistance is directly proportional to length. As the length increases, resistance increases, as a result, current decreases. A good design will minimize heat loss but will increase cost.