FF7/Battle/Damage Calculation

In Attacks, Items, and Weapons there exists a single byte that tells the Battle Engine how to calculate damage. This is a list of known values with their effects on Base Damage. They are classified into Physical, Magical, and Exact. Physical and Magical will rely on the caster's Strength and Magic stat respectively to calculate base damage. After modification it is multiplied by a random variance ([224..255]/256 or something similar). These will also trigger Physical and Magical Counter Attacks respectively. Exact is just what it sounds like. They do not have a base damage calculation. The entire damage comes from exactly the formula shown and is applied to the target without defense calculation (though element is still taken into account). These will not trigger Physical or Magical Counter Attacks, but will trigger General Counter Attacks such as Adamantoise's Light Shell.

For more details, these can be considered Base Damage Modifiers as described in Terence Fergusson's Battle Mechanics FAQ.
Akari has begun a more detailed damage formula page.

Value	Type	Formula [Damage = ]
0x00	None	No Damage Calculation
0x08	Exact	Target's HP & MP * (Strength / 32)%
0x11	Physical	Base * (Strength / 16)
0x22	Magical	Base * (Strength / 16)
0x23	Exact	Target's HP * (Strength / 32)
0x24	Exact	Target's MHP * (Strength / 32)
0x25	Magical	Base + (Strength * 22)
0x26	Exact	Strength * 20
0x37	Physical	Strength * 16; Ignores Barrier; No Base
0x47	Magical	Strength * 16; Ignores MBarrier; No Base
0x50	None	No Damage Calculation
0x60	Exact	User's HP
0x61	Exact	User's MHP - HP
0x68	Exact	Random x 100 (Dice)
0x69	Exact	Number of Escapes
0x6A	Exact	Reduces Target's HP to 1
0x6B	Exact	Number of hours on game clock * 100 + number of minutes in game clock
0x6C	Exact	10 x Target's Kills
0x6D	Exact	1111 x Target's Materia
0x83	Exact	Target's HP * (Strength / 32) if level MOD Attack% = 0
0x96	Exact	User's HP/2
0xA0	Physical	Base * (Strength / 16) * [User's Status Effects See NOTE]
0xA1	Physical	Base * (Strength / 16) * (3 if user is Near-Death, 1 otherwise)
0xA2	Physical	Base * (Strength / 16) * (1 + Dead Allies)
0xA3	Physical	Base * (Strength / 16) * (Target's Level / 16)
0xA4	Physical	Base * (Strength / 16) * (1 + [48 * HP/MHP]) / 16
0xA5	Physical	Base * (Strength / 16) * (1 + [48 * MP/MMP]) / 16
0xA6	Physical	Base * (Strength / 16) * (1 + [AP on Weapon / 10000]) / 16
0xA7	Physical	Base * (Strength / 16) * (10 + [Character's Kills / 128]) / 16
0xA8	Physical	Base * (Strength / 16) * (1 + [Limit Level * Limit Units / 16]) / 16
0xB1	Physical	Base * Strength / 16; No random criticals

NOTE: For A0h base strength, the multiplier is increased by one for the following effects on the user:

• Near-death
• Poison
• Sadness
• Silence
• Slow
• Darkness

and increased by two for the following:

• D.Sentence
• Slow-numb

As an exception to the above rules, 37h and 47h are used as damage calculations for items. Damage to target is calculated normally while ignoring M/Barrier.