need help on grapple

[ShadowMaster]

On page 137 PHB it is stated that grappel check is:

BAB+STR+size

how can I find the BAB of monsters? is it their natural attack that I use in that case?

 

[Chronosome]

There's a big chart in the creature advancement rules (beginning
of the book) whcih breaks down monsters' BAB by type. Keep in
mind any class levels your beastie may have, and you should be fine.

Another way (quick way, for me) is to look at the creature's
first melee attack bonus and then subtract his strength modifier.
Keep feats like Weapon Focus (claw) in mind when figuring things out.

 

[Dr. Zoom]

Look at MM page 13. Each creature type lists how its BAB progresses. It uses the creature's HD instead of levels. For example, the Night Hag is an outsider, so it has fighter BAB. It has 8 HD, so its BAB is +8/+3.