Reach for bigger weapons

[Sissyl]

What reach does a weapon larger than Medium have, in general?

[Fuzzy-Wuzzy]

Reach depends on the size of the wielder but not the size of the weapon. Strange but true.

[SlimGauge]

PRD wrote:

Reach Weapons: Glaives, guisarmes, lances, longspears, ranseurs, and whips are reach weapons. A reach weapon is a melee weapon that allows its wielder to strike at targets that aren't adjacent to him. Most reach weapons double the wielder's natural reach, meaning that a typical Small or Medium wielder of such a weapon can attack a creature 10 feet away, but not a creature in an adjacent square. A typical Large character wielding a reach weapon of the appropriate size can attack a creature 15 or 20 feet away, but not adjacent creatures or creatures up to 10 feet away.

Bolding mine. The weapon itself does not have its own reach, it modifies the user's reach.

There may be (are) corner cases for tiny creatures with reach 0, but you're asking about larger ones.

For large or larger creatures, it depends on that creature's reach. If, somehow, a T-Rex could wield a weapon in those tiny little arms, he'll get less out of it than King Kong would.

Edit: Ninja'd

[Sissyl]

Soooo... A Huge earth elemental wielding a similarly sized dorn-dergar would have a reach of 30'?

[Claxon]

Yeah, in general reach weapons double the reach of the creature using it.

So a large creature with 10ft reach, would threaten 15-20ft with a reach weapon and could not use that weapon to attack 5-10ft.

[Torbyne]

Now a large, or a huge, whip wielder with the whip mastery feat chain starts to look very tempting, doesnt it? :D

[Blymurkla]

I'll refer you to my recent thread on reach. Might help you too.

[Kazaan]

If you need a rationalization for it, reach weapons aren't reach weapons simply because of size, but because of balance. A Longspear is balanced for reaching attacks, but a Longsword is not. So, even if the Greatsword is larger than normal, it isn't going to inflate your reach. Another thing to keep in mind is that an average person's arm is about 2' long. when fully outstreatched. A Medium Longsword is 3.5' long and a Medium Longspear is 8' long. Presuming that the Longsword's actual blade length past the hand is about 3', that means your radius of attack is 5'. But, using something like a Cestus, your radius of attack should be only about 2 feet; yet both weapons have 5' reach in the game. Meanwhile, a Longspear would add about 4-5' to your maximum arm length, meaning an attack radius of 6-7', yet it can fully reach 10' away in the game. Moreover, this is all concerning Medium creatures. A small creature would cut all the radii in half, and yet, a halfling with 1' arms can fully reach out to 5' with a Cestus and 2.5' with a Longsword becomes a full 5'. 3-3.5' with the Longspear becomes a full 10' reach.

Reach is, simply, a mechanic of the game. If the weapon has the Reach property, regardless of its relative size, it allows you to double your natural reach along with setting your normal natural reach as the "minimum" reach. It doesn't matter if it's a Longspear sized for Medium, Small, or Tiny creatures; it still lets you attack out to 10'. It doesn't matter if you wield a Huge Sunblade that's 16 feet long, you can still only attack out to 5' with it as a Medium creature.