pierce

take your grips off, move the brakes/shifters a couple inches inboard, and ride around a parking lot or trail or something, holding the bars at whatever width fieels comfortable. pretend to hold the 'ends' at these imagined widths, and see what works for you. then see how much extra you have.

plan B, have someone measure you from shoulder to shoulder and armpit to armpit, while you're standing up straight with your shoulders back like you're at attention. split the difference, that will be pretty close. 550mm is about 22 inches.

To cut the bars, use a fine tooth hacksaw blade, ideally in a high tension hacksaw frame. If you can, put the bar in a vise (held in with plastic or wood 'v' blocks to prevent scratching) as something that doesn't move is always easier to cut, but I managed to cut mine while it was still attached to the bicycle. I used blue painters tape to mark my cut and as the guide. Take your time with the hacksaw and you'll get a smoother cut (don't force it). I then used a medium smooth cut file to smooth off the end and round the edge of the cut, and I had a little half-round file to take the sharp edges off the inside of the cut too, but thats less important.