Highest Possible Number of Arms by RAW

[Big Lemon]

This is more out of curiosity than for any character I actually plan on making, but using:

1. A humanoid PC race (kasatha)
2. Paizo content exclusively

What is the maximum number of arms I would hypothetically have? As far as I know, only 6 (kasatha alchemist with two vestigial arms), but there may well be additional spells or magic items out there that I'm unaware of that can increase this number to 8 or more.

[DM_Blake]

To answer the thread title:

This.

;)

[Scott Wilhelm]

Vestigial arms don't grant extra attacks, though. There is a psionic class called Aegis which lets you conjure psychic armor which can by level 5 have 2 extra arms that would give you 2 extra attacks. But psionics aren't Paizo.

You could Wild Shape into a Giant Octopus. 8 tentacles with Grab and Constrict. Plus a Bite Attack. Tentacles get a -5 to hit, so take the Multiattack Feat. Take a few levels in Monk, Feral Combat Training and Improved Natural Weapon. Have a suit of octopus-shaped spiked armor made for you, and every grapple will also inflict armor spike damage. Between the strike, the Constrict, and the spikes, that will be sort of like having 25 attacks/round. The damage/round will be embarrassing.

[Scott Wilhelm]

You could be a Kasatha, wear a Mammoth Helm for a Gore Attack, take the Feral Mutagen Discovery for a Bite Attack, wear a Tentacle Cloak for 2 Tentacle Attacks, and Take levels in White Haired Witch for a Hair Attack. You could probably find ways to get Slam and Talon, too.

These aren't multiple arms, but they are multiple attacks

[Konda Immortal]

You could also take the Adopted trait and choose multiarmed. At my house it stacks with a race that already has Multiarmed.

Having six arms and taking the multi-weapon fighting and dual wielding extra attack feats as well as using speed weapons grants 30 attacks on a full attack action.

[Dafydd]

You are all highly UNDER calculating the number of arms you can have.

Synthesist Summoner CAN have 4 at level 1, and at level 20 have 40 arms. This is done by taking Extra Evolution every chance you can, being half elf and putting all those FCB into evo points and turning every evo point into an arm (38 points - 38 arms, +2 free from biped form)

Now, what you do with all those arms is another question entirely.

(Actually, you can use Lesser Evo Surge and Greater Evo Surge to gain more arms, but do you really need more then 40?)

[kestral287]

Half-Elf Summoner (Synthesist if you want the arms yourself) starts with a Biped, takes the Limbs evolution 15 times, has one point to take something else. Thirty-two arms.

Konda Immortal wrote:

You could also take the Adopted trait and choose multiarmed. At my house it stacks with a race that already has Multiarmed.

Having six arms and taking the multi-weapon fighting and dual wielding extra attack feats as well as using speed weapons grants 30 attacks on a full attack action.

That's not how Adopted works. Race traits and Racial traits are not the same thing.

Also, since Multi-Weapon Fighting doesn't have a chain, it + ITWF/GTWF + six arms + full BAB + Haste/Speed (which doesn't stack) =

+18/+18/+18/+18/+18/+18/+18/+13/+13/+8/+8/+3

Twelve =/= thirty.

Even if you homebrewed Improved and Greater Multi-Weapon Fighting, that wouldn't get you to thirty (twenty). Even if you broke the rules on Speed weapons on top of that, that doesn't get you to thirty (twenty-five).