I wear a size 26.5, and I'm 5'9" with a 29 inch inseam. You might try asking some of your fellow dojo members if you can try on their hakama to help you decide what size to get. Also, try and find someone who has the same inseam as you ask them their size.
Thanks - the real problem is that dif. manufacturers use slightly dif. numbers.... I have an older Bujin heavy denim hakama that is noted as one size, another old kendo hakama I've been using for over 20 years, that's another size.... etc.... Tozando seems to use their own system, close but not exactly the same as some others....