What are phonetic components in kanji?

A large share of kanji are built from two parts: one that hints at meaning and one that hints at sound. These are called phono-semantic compounds (形声文字, keisei moji). Once you spot the sound part, you can often guess a new kanji’s on’yomi.

What does a sound family look like?

Sound part	Kanji	On’yomi	Meaning part
青 (セイ)	晴	セイ	日 sun: clear weather
	清	セイ	氵 water: pure
	精	セイ	米 rice: refined
	静	セイ	quiet
化 (カ)	花	カ	艹 plant: flower
	貨	カ	貝 shell/money: goods
工 (コウ)	紅	コウ	糸 thread: crimson
	功	コウ	力 power: merit

The meaning part is usually the radical. The other part carries the sound.

How reliable is it?

Useful, not perfect. Sounds changed over centuries, so some members drift: 青 gives セイ in 晴, but 情 is ジョウ as well as セイ. Use the sound part as a first guess, then check.

It also only helps with on’yomi. Kun’yomi are native Japanese words and don’t follow the sound part. More on that split in on’yomi vs kun’yomi.

How to use this for JLPT study

1. When you learn a new kanji, ask: do I know another kanji with this part? Do they share a reading?
2. Group them in review. Seeing 晴, 清, 精 together makes the family stick.
3. In a mnemonic story, let the meaning part drive the picture and keep the sound part as a recurring character.

For the JLPT kanji reading task, a good guess can rule out two of four options. See how kanji are tested on the JLPT.

Kanji Mnemonics (my app, so weigh my opinion accordingly) covers N5 through N1 with one keyword, one story and one picture per kanji, readings and example words, a flashcard quiz in both directions and progress per level. It works offline. Lesson 1 is free; the rest needs Pro (weekly, monthly or yearly subscription, or a one-time lifetime purchase). See the app page, the App Store listing or all my apps.