When dealing with stiff shelled top hats and bowlers, unlike soft headwear (e.g. fedoras and tweed caps), the head shape is as important as the size. Hats usually come in regular oval shape, but heads are irregular, a lot of people tend to taper towards the forehead, so the width of the head is bigger at back. A full fitting prior to buying a hat is recommended so your shape can be measured using specialised tools such as a conformateur and formillion. If you have already bought a hat or inherited a hat elsewhere we can usually assist, provided that it is in good condition and the correct size.
Please note that over the last century heads have become bigger, to find a silk hat to fit is getting harder as less large sizes were made many years ago. The average hat size is now about size 59cm, and unfortunately vintage silk top hats typically cannot be 're-sized' or stretched, but only 'reshaped'.