Radicals are 214 combinations of well-defined sets of strokes that have a ‘basic’ meaning. For example:

meaning
one
two
person, human

meaning
power
rice field
rain

All the examples above are both radicals and kanjis; this is not the general case, though. Not all radicals are kanjis, e.g., the radical 亻, which like 人 means ‘person’ or ‘human’, is not a kanji, while the kanji 花, which means ‘flower’, is not a radical. Radicals that are not kanjis are called ‘free radicals’ and only show up as components of a more complex character, e.g., the human legs radical 儿, the plant radical 艹, the long stride radical 廴, and many others.

Although a kanji may be composed of many radicals, only one of those radicals gives it its general meaning, or ‘flavor’. Thus, we can classify any kanji according to this one radical it has. Actually, radicals were originally selected to classify and index the kanjis in the kangxi dictionary, published in 1716. Still today, some Japanese and Chinese dictionaries are organized by radicals.

Besides being able to use radical-based dictionaries, learning radicals is useful because they are a basic blocks of all kanjis. We can view kanjis as a random set of meaningless strokes, and learn them the hard way, by repetition, or we can view them as an organized set of meaningful components, each one adding some meaning to the kanji, which is much easier.

We often refer to the radicals by number. In the tables below, the number of a radical in a given row and column, i.e., (row, column), is

radical No. = (row × 10) + column

Thus, for example, the radical for ‘mountain’, , is in (4,6), i.e., row 4, column 6, so it is radical 46, and the radical for ‘water’, , is radical 85, so we will find it in (8,5), i.e., row 8, column 5.

The following are the 214 kangxi radicals, ordered by their number of strokes (wikipedia, unicode):

Overwhelming? Yes… at first sight. However, they are a huge help in understanding and writing kanjis and, unlike the kanas, there is no good reason to learn them all at once.