Four Yuga are collectively known as 'Chaturyuga'. A Brahma's day consists of one-thousand such 'Chaturyugas'. Altogether, fourteen Manu appear during this whole period of 1000 Chaturgas or in other words a day of Lord Brahma. Each 'Manvantar' is named after a Manu and is equivalent to little more than 71 Chaturyugas. It also has its own Indra, Saptarishis and other deities. This way, a manvantar is also equivalent to 8,52,000 years of the deities or divine years. Going by the standard of the years of this world a manvantar is equivalent to 30,67,20,000 years. On the basis of the years of this world, so a Yug is equivalent to 30,67,20,000 x 14 = 4,29,40,80,000 yrs. ............

Dependns on god

wse wse...jse jse..yug...badalta hai..saal ghattte jate hai...

at last..the whole world will be ended...nd re furnished

Every Yuga has different duration:
The traditional timescale of the yugas is as follows:
Satya Yuga or Krita Yuga - 1,728,000 years
Treta Yuga - 1,296,000 years
Dvapara Yuga - 864,000 years
Kali Yuga - 432,000 years

Source: wiki

Many others like Aurbindo Ghosh have stated that Kali Yuga is now over. The Kali Yuga is sometimes thought to last 432000 years