The first anime series (1997) covers Black Swordsman arc (volume 1-3) until just before the end of Golden Age arc (volume 3-13). However, it includes original episodes and some modifications to the original story. (Source: Yahoo! Chiebukuro (Japanese))
The OVA (or 3-part movies) covers the whole Golden Age arc, which is volume 3-14, hence the name Berserk: The Golden Age Arc.
The second anime series (2016) covers the beginning of Black Swordsman arc (chapter 1&2), omits the whole Golden Age arc, then continues on Conviction arc (volume 14/chapter 115 - volume 21) until Falcon of the Millenium Empire arc (volume 22~)
For additional reference, the manga is still on-going (volume 39) as of now. The story arcs:
- Black Swordsman: Volume 1-3
- Golden Age: Volume 3-14
- Conviction: Volume 14-21
- Falcon of the Millennium Empire: Volume 22-35
- Phantom World (Fantasia): Volume 35~
References: