Calculations listed below are unofficial and based off The Math of DSO & Max Resist and Armor and through observation.
Base Damage Per Level
Check the base damage per level for your class in this > Article
Armor / Resistance
Items and gems add to the numerical value of armor and resistance, which is then converted to an effective percentage value versus an enemy of a specific level or on a specific Infernal mode. This generic formula calculates the % values:
f(value) = value / [ value + Φ(level)] * 100
 Φ(40) = 1556 (max 80%=6224)
 Φ(45) = 1919 (max 80%=7676)
 Φ(50) = 2370 (max 80%=9480)
 Φ(55) = 6398 (max 80%=25585)
 Φ(Infernal1) = 7679 (max 80%=30716)
 Φ(Infernal2) = 8958 (max 80%=35832)
 Φ(Infernal3) = 10240 (max 80%=40960)
Block Rate / Critical Rate
 f(50) = 110,95 (max 80%=8876)
 f(55) = 200 (max 80%=16000)
Level 50 players can use the amended formula:
f(value) = value / 110,95
Block Strength
Block Strength to Percentage
P = 100  (100/BS)
Percentage to Block Strength
BS = 100 / (100P)
Attack Speed
The base attack speed of all classes (without weapons) is 1.00 attacks / second. Equipping a weapon will override the default speed with the weapon's speed. Attack speed can be increased through weapon / item enchantments, Sapphire gems, and Knowledge talent bonuses. Add all +% speed bonuses (except the weapon's speed enchantments) then multiply by the speed of the weapon to calculate the bonus to attack speed.
(weapon's base attack speed + (weapon's base attack speed * sum of all attack speed boosts)) = attack speed
If the weapon doesn't have attack speed enchantments this formula is enough, but if the weapon has attack speed enchantments additional two steps are required:
attack speed * weapon's attack speed enchantment = weapon's enchantment speed bonus
attack speed + weapon's enchantment speed bonus = final attack speed (attack/second)
Check the Skill Animation Timing Table.
Travel Speed
Many factors alter travel speed and some are conditional (e.g. limited to location or actions). Here are common travel boosts:
 Fairysummoning Wand: +25% (in urban areas)
 Mounts: +70% (dismounted when attacking/attacked; limited arena use)
 Epic Mounts: +100% (dismounted when attacking/attacked; limited arena use)
 Mythical Mounts: +120% (dismounted when attacking/attacked; limited arena use)
 Knowledge Tree: 1% per spent knowledge point, max. of 25%
 Equipment travel speed bonus:  (effective at all times)
Travel speed increases are summed up and can be stated as a percent increase compared to normal speeds:
100% * (sum of % travel speed bonuses) = % travel speed increase
Calculating Golden Value on Base Stats
You can calculate the starting golden values on item's base stats by using the following formula:
Gs = Vmin + ((Vmax  Vmin) 10%)
Gs  the starting value for golden base value
Vmin  minimum possible base value
Vmax  maximum possible base value
Example: If we calculate Gs for critical hit value on T5 Mortis' Ring of Death we get:
Vmin=880
Vmax=1160
Gs=880+((1160880)10%)
Gs=1132 (meaning all stats between 1132 and 1160 are highlighted as golden)
Some items like all weapons and some quivers and weapon adornments, are having separate Gs for min and max value. In such cases we can calculate separate Gs for each range:
G1s = V1min + ((V1max  V1min) 10%)
G2s = V2min + ((V2max  V2min) 10%)
Note: if the enchantments are close to the limit the formula will not work because in game we can only see the rounded but not the real values.
Knowledge Tree Damage Bonus
Behemoth talent add a +50% bonus on the weapon damage and does not apply to total damage. The damage bonus will then be multiplied by 2% for each level in your Attack to arrive at the final damage boost.
Upgrading with Glyphs
The percentage value with which absolute enchantments will increase with a +1 level upgrade depends on the item level: Source. For a list of the maximum enchantments of each item click HERE.



Online Calculators
DSO Weapon Optimizer (Outdated) by Charles de Silva
Damage Performance Index by Unknown
Output enchantment probabilities 2.0 Crafting by Armando76
Drakensang Optimizer (Outdated) by Sharlaan Heredur