From Diablo Wiki
Rubies are one of the four types of gems found in Diablo III.
Rubies are very useful socketed in weapons, especially since the Patch 1.0.7 buffed their damage. Prior to that patch Rubies were great in weapons for low and mid-level characters, since the damage added by the Ruby was very substantial. Rubies were not as useful for high level characters, since with better gear and increased Critical hit Chance stats, the Emerald with its Critical hit Damage bonus was much more powerful than the Ruby.
Rubies are coveted by Barbarians, since the +Strength bonus adds to their damage output.
Rubies are also very popular for the +%experience gain when socketed in helms. This bonus became much more popular after Patch 1.0.4 when the Paragon system was introduced and gaining experience from kills became a key preoccupation of level 60+ characters.
 Development Changes
During development, Rubies added a bonus to the Attack stat, when socketed in "other" objects. This was changed to a +Strength bonus in the final game.
 Ruby Stats
 Diablo II Ruby
Though, their stats are not the same as Rubies in Diablo III.
|Quality||Weapon||Helm or Armor||Shield||Clvl Req|
|Chipped||+3-4 Fire Damage||+10 to Maximum Life||+12% fire resistance||1|
|Flawed||+5-8 to Fire Damage||+17 to Maximum Life||+16% to Fire Resistance||5|
|Normal||+8-12 to Fire Damage||+24 to Maximum Life||+22% fire resistance||12|
|Flawless||+10-16 to Fire Damage||+31 to Maximum Life||+28% fire resistance||15|
|Perfect||+15-20 Fire Damage||+38 to Maximum Life||+40% fire resistance||18|
 Patch 1.0.7 Buffs
- Chipped Ruby: +3 minimum damage/+3 maximum damage (up from +2/+2)
- Flawed Ruby: +6 minimum damage/+6 maximum damage (up from +4/+4)
- Ruby: +9 minimum damage/+9 maximum damage (up from +8/+8)
- Flawless Ruby: +12 minimum damage/+12 maximum damage (up from +10/+10)
- Perfect Ruby: +15 minimum damage/+15 maximum damage (up from +11/+11)
- Radiant Ruby: +18 minimum damage/+18 maximum damage (up from +12/+12)
- Square Ruby: +21 minimum damage/+21 maximum damage (up from +13/+13)
- Flawless Square Ruby: +25 minimum damage/+25 maximum damage (up from +14/+14)
- Perfect Square Ruby: +30 minimum damage/+30 maximum damage (up from +15/+15)
- Radiant Square Ruby: +40 minimum damage/+40 maximum damage (up from +16/+16)
- Star Ruby: +60 minimum damage/+60 maximum damage (up from +17/+17)
- Flawless Star Ruby: +80 minimum damage/+80 maximum damage (up from +18/+18)
- Perfect Star Ruby: +100 minimum damage/+100 maximum damage (up from +19/+19)
- Radiant Star Ruby: +130 minimum damage/+130 maximum damage (up from +20/+20)
- Marquise Ruby: +160 Minimum and +160 Maximum Damage
These rubies have also had their bonus damage calculations changed, and will now add damage flatly to both the minimum and maximum values on weapons
For example, if you have a weapon that does 150-200 damage and you socket a Perfect Square Ruby (which adds +30 minimum damage/+30 maximum damage), your weapon will do 180-230 damage
The boosts to high end Ruby damage were enormous, and while Emeralds remain the weapon socket of choice for most characters, Rubies are useful for some classes and builds, especially those that deal damage with skill that do not or seldom proc their damage from critical hits.
|Items of Diablo III  Item Basics Normal Items Legendary Armor I Legendary Armor II Legendary Weapons 1h Legendary Weapons 2h Item Sets|
|Item Basics||Item Modifiers||Inventory||Artisans||Merchants||Miscellaneous |
|Armor - Class-Specific||Weapons - Class-Specific||Crafting Items||Other Items |
|| • Blacksmith Plans
|Waist||Wrists & Hands||Legs & Feet||Head |
|| Voodoo Masks - WD|
| Chest Armor
|| Amulets cont.
|| Rings cont.
40) Puzzle Ring
|| Sources - Wiz|
|| Fist Weapons - Monk
|| Mighty Weapons - Barb|
|| Daibos - Monk
|| Bows |
|Item Sets |