The ideal length for an auxiliary cable depends on where and how you’ll be using it. 3ft would be enough for connecting headphones and smartphones while on the go. For use in cars or at home, choose one that’s 4ft to 7ft long. If you’re connecting a device to your car stereo from the front seat, 4ft would suffice. If you’re likely to connect devices from the back seat, choose cables that are longer than 6ft.