A useful utility to convert between old Japanese units (Shakkan-Ho) and the good old Metric and Imperial Systems.
One shaku (尺) is approximately 30cm. One sun (寸) is about 3cm, while one bu (分) equals 3mm. As a curiosity, one ken is equivalent to 6 shaku (180cm), approximately the height of a man.
Even when Shakkan-Ho is the old system, it's still used in Japanese martial arts for measuring the length of weapons, as well as for clothing (in which case a bu corresponds to 3.79mm) and footwear (when it corresponds to 2.4mm.) In any case, one shaku always equals to ten sun; and one sun contains always ten bu.