Somebody (hi, mmadsen) asked about them so here are my house rules for hp and damage. Feel free to rant
My premises in creating them were the following (if you change one aspect of the game, several others have to be reconsidered as well):
* hp should reflect actual wounds, blood loss and pain and do not increase with level (except for Con increase, Toughness feat or multiclassing)
* higher level characters become harder to hit instead, as long as they are aware of the attack (i.e they gain a dodge bonus to AC depending on level)
* while armor makes people harder to hit, it also absorbs some damage
* if hp do not scale with level, neither should damage/healing spells
* the changes should be easy to implement, so the rules changes mostly concern calculations made before game sessions (granted, you have to remember Dodge bonus and DR more often, but these are core mechanics after all)
I haven't playtested these rules for very long, but so far they work quite well for my group. However, the PCs are currently 4th level, which means that they had more hp so far than with the regular rules. The ``interesting times'' have just begun for them...
And I should add that these rules were inspired by Ken Hood's Grim'n'Gritty HP rules. So thank you, Ken!
Hitpoints
Any creature has base hp equal to its Con score plus maximum points for a single HD. The result multiplied by a factor depending on size (round down, minimum 1). Creatures without a Con score use Wis instead, those with multiple HD types take their best one.
Size..........Multiplier..Example.........Con...HD...hp
Fine to Small....*........Kobold.(1/2.HD)..11...d8....9
Medium...........1........Human.commoner...11...d4...15
Large............2........Hill.giant.......19...d8...54
Huge.............4........Cloud giant......23...d8..124
Gargantuan.......8........Purple worm......25..d10..280
Colossal........16........Great red wyrm...27..d12..624
* Use the number of HD of the base creature or 1, whichever is worse.
(aka ``not giving haflings the shaft'' rule)
Natural healing: A creature recovers three times the given multiplier in hp per day of rest, modified as usual for medical treatmentn and quality of rest.
Death from hp loss: A creature dies if its hp reach -Con, regardless of size. Stabilization rolls are made on the dying creature's turn.
Death from massive damage: This rule is obsolete for most creatures of medium size or smaller, but may be useful for defeating larger opponents. To account for reduced spell damage (see below), the optional rules for ``death from massive damage based on size'' are not being used, i.e. the threshold is always 50 points of damage from a single attack.
Toughness: The feat Toughness works normally (add 3 hp after the size multiplier) and may still be taken multiple times.
Defense Bonus
Instead of increasing their hp, experienced characters and creatures become harder to hit. This is reflected in their defense bonus (DB), a level-dependent dodge bonus to AC. Any class with either a good BAB progression (+1 per level) or a good Reflex save also uses the good DB progression given below, while all other classes use the bad progression. Multiclass characters add together the bonuses for their classes as usual.
Example: A wizard 4/fighter 2 gains a +2 defense bonus to AC: +1 from having 4 levels as wizard using the bad progression and +1 from having 2 levels as fighter using the good one.
(omitted the table: good progression is 1/2 class level and bad progression is 1/3 class level, both rounded down)
DR from Armor
Armor does not only make a character harder to hit, it also reduces the damage from taking a blow somewhat:
Protection..........DR
Light.armor.........1/-
Medium.armor........2/-
Heavy.armor.........3/-
Magical.armor*.....+1/- per +1 enhancement bonus
Natural armor......+1/- per 4 full points
* Only actual armor, not shields, etc.
DR from other sources is added to these figures.
Example: Consider an 11th level barbarian wearing leather armor +1 and bracers of armor +5. The AC bonuses from the armor and bracers do not stack, so his AC modifier from gear is +5 for the bracers. Still, wearing the armor is useful, as it also grants DR 2/- due to its magical bonus, for a total DR 3/- (including the barbarian's own DR 1/-).
Magic and Special Effects
Magical and other special effects that cause or heal damage are rescaled to fit revised hp:
Attack Spells: If the damage or hp loss caused by a spell depends on caster level, use the spell's level +2 instead. The same holds if a spell allows for multiple attacks or causes damage for a period of time determined by caster level. Other spell effects still depend on caster level.
(using straight caster level makes combat magic too wimpy, IMO - who would use burning hands for 1d4 damage if even a commoner has 15 hp?)
Example 1: Shocking grasp always causes 1d8+3 points of damage (spell level 1 + 2 = 3).
Example 2: Magic missile creates two missiles per casting (spell level 1 + 2 = 3).
Example 3: Melf's acid arrow causes 2d4 points of damage on a hit and on the following turn (spell level 2 + 2 = 4 for one extra turn).
Healing Magic: If the damage recovered or temporary hp gained from a spell depend on caster level, use the spell's level instead. As above, all other spell effects still depend on caster level.
Example 1: Cure medium wounds cast by a cleric heals 2d8+2 points of damage (spell level 2). However, the spell inflicts 2d8+4 points of damage on any undead creature, as it counts as attack spell in this case (spell level 2 + 2 = 4).
Example 2: Among other effects, Tenser's transfromation grants 6d6 temporary hp (spell level 6).
Domain Powers: The +1 bonus to caster level granted by certain domains serves to increase spell effectiveness even if this is now based on spell level.
Magical or Supernatural Effects: Halve the number of dice of damage cured, granted or inflicted by any magical or supernatural effect that is not a spell (round down, minimum 1).
Example: All flaming burst weapons deal 1d10 extra fire damage on a critical hit, regardless of the weapons critical multiplier.
Sneak Attacks: The damage bonus from the sneak attack special ability is equal to the sum of class levels of all classes that grant this ability.
Example: A rogue 8/assassin 2 deals an extra 10 points of damage with a sneak attack.
Other Damage: Weapons and natural hazards deal normal damage. Falling damage is multiplied by a creature's size multiplier for hitpoints, however.

My premises in creating them were the following (if you change one aspect of the game, several others have to be reconsidered as well):
* hp should reflect actual wounds, blood loss and pain and do not increase with level (except for Con increase, Toughness feat or multiclassing)
* higher level characters become harder to hit instead, as long as they are aware of the attack (i.e they gain a dodge bonus to AC depending on level)
* while armor makes people harder to hit, it also absorbs some damage
* if hp do not scale with level, neither should damage/healing spells
* the changes should be easy to implement, so the rules changes mostly concern calculations made before game sessions (granted, you have to remember Dodge bonus and DR more often, but these are core mechanics after all)
I haven't playtested these rules for very long, but so far they work quite well for my group. However, the PCs are currently 4th level, which means that they had more hp so far than with the regular rules. The ``interesting times'' have just begun for them...
And I should add that these rules were inspired by Ken Hood's Grim'n'Gritty HP rules. So thank you, Ken!
Hitpoints
Any creature has base hp equal to its Con score plus maximum points for a single HD. The result multiplied by a factor depending on size (round down, minimum 1). Creatures without a Con score use Wis instead, those with multiple HD types take their best one.
Size..........Multiplier..Example.........Con...HD...hp
Fine to Small....*........Kobold.(1/2.HD)..11...d8....9
Medium...........1........Human.commoner...11...d4...15
Large............2........Hill.giant.......19...d8...54
Huge.............4........Cloud giant......23...d8..124
Gargantuan.......8........Purple worm......25..d10..280
Colossal........16........Great red wyrm...27..d12..624
* Use the number of HD of the base creature or 1, whichever is worse.
(aka ``not giving haflings the shaft'' rule)
Natural healing: A creature recovers three times the given multiplier in hp per day of rest, modified as usual for medical treatmentn and quality of rest.
Death from hp loss: A creature dies if its hp reach -Con, regardless of size. Stabilization rolls are made on the dying creature's turn.
Death from massive damage: This rule is obsolete for most creatures of medium size or smaller, but may be useful for defeating larger opponents. To account for reduced spell damage (see below), the optional rules for ``death from massive damage based on size'' are not being used, i.e. the threshold is always 50 points of damage from a single attack.
Toughness: The feat Toughness works normally (add 3 hp after the size multiplier) and may still be taken multiple times.
Defense Bonus
Instead of increasing their hp, experienced characters and creatures become harder to hit. This is reflected in their defense bonus (DB), a level-dependent dodge bonus to AC. Any class with either a good BAB progression (+1 per level) or a good Reflex save also uses the good DB progression given below, while all other classes use the bad progression. Multiclass characters add together the bonuses for their classes as usual.
Example: A wizard 4/fighter 2 gains a +2 defense bonus to AC: +1 from having 4 levels as wizard using the bad progression and +1 from having 2 levels as fighter using the good one.
(omitted the table: good progression is 1/2 class level and bad progression is 1/3 class level, both rounded down)
DR from Armor
Armor does not only make a character harder to hit, it also reduces the damage from taking a blow somewhat:
Protection..........DR
Light.armor.........1/-
Medium.armor........2/-
Heavy.armor.........3/-
Magical.armor*.....+1/- per +1 enhancement bonus
Natural armor......+1/- per 4 full points
* Only actual armor, not shields, etc.
DR from other sources is added to these figures.
Example: Consider an 11th level barbarian wearing leather armor +1 and bracers of armor +5. The AC bonuses from the armor and bracers do not stack, so his AC modifier from gear is +5 for the bracers. Still, wearing the armor is useful, as it also grants DR 2/- due to its magical bonus, for a total DR 3/- (including the barbarian's own DR 1/-).
Magic and Special Effects
Magical and other special effects that cause or heal damage are rescaled to fit revised hp:
Attack Spells: If the damage or hp loss caused by a spell depends on caster level, use the spell's level +2 instead. The same holds if a spell allows for multiple attacks or causes damage for a period of time determined by caster level. Other spell effects still depend on caster level.
(using straight caster level makes combat magic too wimpy, IMO - who would use burning hands for 1d4 damage if even a commoner has 15 hp?)
Example 1: Shocking grasp always causes 1d8+3 points of damage (spell level 1 + 2 = 3).
Example 2: Magic missile creates two missiles per casting (spell level 1 + 2 = 3).
Example 3: Melf's acid arrow causes 2d4 points of damage on a hit and on the following turn (spell level 2 + 2 = 4 for one extra turn).
Healing Magic: If the damage recovered or temporary hp gained from a spell depend on caster level, use the spell's level instead. As above, all other spell effects still depend on caster level.
Example 1: Cure medium wounds cast by a cleric heals 2d8+2 points of damage (spell level 2). However, the spell inflicts 2d8+4 points of damage on any undead creature, as it counts as attack spell in this case (spell level 2 + 2 = 4).
Example 2: Among other effects, Tenser's transfromation grants 6d6 temporary hp (spell level 6).
Domain Powers: The +1 bonus to caster level granted by certain domains serves to increase spell effectiveness even if this is now based on spell level.
Magical or Supernatural Effects: Halve the number of dice of damage cured, granted or inflicted by any magical or supernatural effect that is not a spell (round down, minimum 1).
Example: All flaming burst weapons deal 1d10 extra fire damage on a critical hit, regardless of the weapons critical multiplier.
Sneak Attacks: The damage bonus from the sneak attack special ability is equal to the sum of class levels of all classes that grant this ability.
Example: A rogue 8/assassin 2 deals an extra 10 points of damage with a sneak attack.
Other Damage: Weapons and natural hazards deal normal damage. Falling damage is multiplied by a creature's size multiplier for hitpoints, however.
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