刚好 (gānghǎo) is an adverb or adjective meaning "just right," "exactly," or "happens to be." It indicates that something fits perfectly or occurs at precisely the right moment, amount, or degree — neither too much nor too little.
这双鞋的大小刚好合适。
Zhè shuāng xié de dàxiǎo gānghǎo héshì.
These shoes are just the right size.
我刚好有空,一起去吃饭吧。
Wǒ gānghǎo yǒu kòng, yīqǐ qù chīfàn ba.
I happen to be free — let's go eat together.
钱刚好够买两杯咖啡。
Qián gānghǎo gòu mǎi liǎng bēi kāfēi.
The money is just enough to buy two cups of coffee.