The thing is, it very much depends on your body shape, the size of your head and your height. So to give you one straight answer is a little bit difficult. I have applied so many sets of clip-in hair extensions over the years, all 50cm long, but on some people they fall a few cm below the bra strap and on others they reach right down to their tail bone. So here is what you can do to measure how long 50cm hair extensions will be on you. Grab a tape measure and measure 50cm from the middle of your ear. Bring the tape measure over your shoulder, so you can see exactly where your hair extensions will come down to. You can ask someone to help you measure at the back if you want to know how far down your back they will hang.