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Physical Properties and Measurement

Grouping by Length/Width Ratio

There are several methods of describing the configuration of a rice grain, the most common of which is to use the ratio between the length and width of a rice grain. For example, short grain (type A, equivalent of japonica, major line of Japanese rice), large grain (type B, equivalent of javanica, upland and European lines) and long grain (type C, equivalent of indica, Chinese line)

Traditionally in Japan, we have used the grouping method of long grain having a 1.8 or higher length/width ratio, medium grain between 1.6 and 1.79, and round grain less than 1.59. Similarly, the testing criteria for imported rice in Japan define a grain with having a 2.0 or less in length/width ratio for a round (bold) grain, while greater than 2.0 or indica with less than 2.0 for long grain.

On the other hand, the International Rice Research Institute (IRRI) uses the grouping standard for a rice variety configuration as shown in Table 2. According to this standard, almost all Japanese varieties are grouped as a medium round grain of the short type, while those of Thailand and India are mostly extra-long type or thin grain of long type.