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This method is fiddlier than both methods I used in the past but it seems to give a lot better results. I do use it on the fly.
“Monsters” are creatures that don’t have a stat line (str, dex etc), that just have HD, AC, and attacks.
If you have the same creature in your monster manual you can use that if you want.
Otherwise, use the “oHD” header based on their original HD in the table below to find the correct row for them.
Their AC is not in the table. It’s going to be 18 minus their 1e AC.
To figure out how much damage they deal now, compare the total amount of damage dice total in the 1e version with the version listed under #AT here. For example d4/d4/d6 is 1e’s version of saying there’s three attacks, each with one dice, and 2×2 here means there’s two attacks, each with two dice. The first number is the number of attacks.
If the total number of dice is already the same or higher in 1e, you’re good; otherwise change it to have as many dice as this new #AT number. In this example, three is fewer than four so add one die to one of the attacks, the last one for example.
Add the bonus from the “mod” column to each attack. So in our example, an oHD 4 monster with 1d4/1d4/1d6 becomes 1d4+3, 1d4+3, 2d6+3.
The total amount of dice is what matters for this step; what ever die size your 1e module says is fine, as is the fact that some monsters will hit twice at 2d6+3 while others four times at 1d6+3 per hit, or some one hit at d6+3 and other sneak attack hit at 3d6+3. That’s all good and gives variety to the opposition.
Their ability modifier (sans proficiency) for both constitution and their main attacking ability is listed under “mod”. Halve that for their other four abilities, if needed.
The †and ‡ symbols are redundantly there to remind me that some of the attacks need more than one die, as explained above. (Unless they have a great sword or maul, these extra dice aren't necessarily part of the weapon. It can be explained by abilities like Lunging Attack, Brute, Sneak Attack etc.)
Their hit bonus is listed under AV. AV 15 means that they hit with +5.
The HP is what you add to their existing 1e HP, based on their new HD (listed under nHD) and their constitution modifier (listed under Mod). The XP value is for 5e.
So if they meet a gal in the dungeon who’s listed as HD 4, she becomes a level 6, HD 6 person after conversion.
oHD #AT Mod AV HP nHD XP 1 1 +1 13 +6 2 50 2 1 +2 14 +10 3 100 3 2 +3 15 +16 4 200 4 2×2 +3†16 +27 6 450 5 2×2 +4†17 +37 7 700 6 2×2 +4†17 +41 8 700 7 2×3 +4‡ 18 +45 9 1100 8 2×3 +4‡ 18 +49 10 1100 9 3×3 +4‡ 18 +53 11 1800 10 3×3 +4‡ 18 +63 12 2300 11 3×3 +4‡ 19 +61 13 2300 12 3×3 +4‡ 19 +73 15 2900 13 3×3 +4‡ 19 +77 16 3900 14 3×3 +4‡ 20 +81 17 5000 15 4×3 +4‡ 20 +85 18 5900 16 4×3 +4‡ 20 +89 19 7200
For hit dice 17 or higher, their new HD is going to be three more, so you can calculate their new hit point value by 8.5(HD+3) and then looking up appropriate stats in a 5e book like Forge of Foes or similar.
For HD less than one, don’t add anything. They’re fine the way they are. Mod is 1 and attack value is 13. XP is 25, 10, or even 0 depending on the situation.
Let’s say they’re fighting a Frobnicator and you don’t have that or a similar monster in your 5e manuals, so you have to convert it.
SZ L; AL N; AC 5; MV 120; HD 6; HP 39; #AT 6; Dmg 1–6/1–6/1–6/1–6/1–6/1–6.
You look up 6 in the oHD column here and find that its new HP is 80, since 39+41 = 80. You can also see that it is now an 8 HD monster, which normally doesn’t matter, but it’s there just in case you’re like my group and it ends up mattering in some weird situation.
The AC is 13, you don’t need a table for that.
You can see in the table that the attack value is 17 and since 1–6 is 1e’s weird way of writing d6, each attack should deal 1d6+4. You don’t need to make that 2d6+4 since six attacks is already more than the minimum four (2×2).
The XP value is 700. Kind of low for what ended up beefier than an owlbear but there you go.
If it instead had been an Emulsifier that they’re fighting with same stats except #AT 2; 1–4/2–8, and knowing that that’s how 1e writes 1d4 and 2d4, respectively, then that’s one die short of our goal of 2×2, so make both attacks 2d4+4. Nice!
By “people”, I mean creatures that have a stat line. They already have a con, a str, a dex…
Converting people is a chore so if you wanna treat them like monsters and just scroll up, I don’t blame you. I mostly use the “monsters” conversion method even for people.
Look up their HD in the nHD column instead of the oHD column.
All you’re getting from the row is their XP value, their number of attacks, and their dice per attack.
Don’t look at the oHD, mod, AV, or HP columns.
You’ve already got their ability mods. Add their proficiency bonus to their main stat to find their tohit value (and then add eight to that for their save DC or ten to that for their AV, if you’re using the “attack value” house rule).
The proficiency bonus is based on nHD if you bumped it and oHD if you didn’t. It’s (Level+7)/4, so HD 1–4: +2, HD 5–8: +3, HD 9–12: +4, HD 13–16: +5, HD 17–20: +6.
Add their con bonus times their HD to their HP. Or just add con to 4.5 and multiply that by the current HD.
An AC of 18 minus 1e AC makes for good gameplay at these these high hit point and damage values, but it doesn’t make sense for an AC 13 guy to then have been revealed as wearing chain mail when the party takes his gear after the fight. 21 minus 1e AC matches up with most of the 1e armor types.
So you have two options.
AC 18 minus 1e for fun gameplay but confusing for looting sticklers.
Or, use 18 minus 1e for monsters and for plate, splint, and chain (reading that as “halfplate”, “breastplate”, and “chain shirt” respectively) but 21 minus AC for other armor types.
The 1e PHB didn’t have chain shirts or half plates or breastplates. These lower ACs are more fun to fight against.
Everyone loves Jayani al-Jasir on the corsair council in the free city of Hawa.
She is a a human level 14 fighter. The armor is specified (an unusually strong set of Bracers of Defense) and it’s not chain/splint/plate, so we’ve got to use the 21 rule, which, since she has AC 0 descending, her AC is 21. Her constitution is 14 in 1e, which is +2 in 5e, so 1d8+4 times her level of 14 is 84. (Pretty spot on to the listed 1e HP which was 82.)
She has dex +3, and at level 14 her proficiency bonus is +5 so she hits at +8 or AV 18. (When she’s using her magic +2 knife, it’s +10 or 20.) So far, we haven’t had to check our table. We only do for her XP value (which is 2300) and her number of attacks, which is 3×3 according to my table here. Since she is a fighter, that’s good. Die type according to weapon type, so if she hits with her shortsword, that’s 3d6+3. I guess she has some battlemaster-like ability of using extra dice. With her magic knife, it’s 3d4+5, since three from her dex and two from the knife magic makes five.
So to recap, 5e changed her attack value (she has THAC0 7 in 2e, which would indicate +3, but 5e makes that +8 because of dexterity and proficiency) and her damage output (she already had three attacks in 2e but here she gets extra dice on her hits).
Sometimes you see “AC as Plate+Shield”, “AC as leather” etc. Taking that by their word, that means:
The game (and that game was LotFP 🤕) that originated that convention use 14 for leather, 16 for chain, and 18 for plate, but that game deliberately went for a harder-to-hit, lower-HP feel that suits a “HP is meat points” style. In 5e where HP is more fatigue and the real danger is death save fails & lingering injuries, lower values work better.
Some OSR games already have an ascending AC in square brackets. Those are fine. For the stickliest of the sticklers: Those square bracket values like 5 [14], are one step too high for "monsters" and for our new "chain shirt", "breast plate", "half plate" philosophy, but are correct for low-armored "NPC"s like unarmed or leather. But that only affects five percent of all rolls. Just be consistent about how you do it and don't be like "aaaah I really want them to hit this one"—that's not right. Be consistent & objective.
The reason for that discrepancy is that the B/X armor table is the same as 1e at chain & higher but B/X is harder to hit than 1e at lower values like unarmored and leather. So normally people subtract from 20 or 21 for 1e, and from 19 for B/X. But I’ve found again and again that in playtesting that we want a lower AC, higher HP feel. Working with monster books like the SRD, the Forge of Foes, and the Monstrous Menagerie, and discussing with my own players after several hundreds of sessions, I feel like 18 is the better value.
Stan Shinn made homebrew conversions rules when 5e was still in playtest and called “next”, and updated them when the real game came out. We used them for B4 The Lost City and it was good. Most of the monsters, we’d use the 5e version of, when available, but still. Nice to have.
Then the official conversion rules came out and I switched to them right away. They were a lot simpler and I didn’t need a table, I can do it in my head (AC is 19-(b/x AC) or 20-advanced AC, tohit is 2+half HD, damage & HP is unchanged, super low for 5e) and we used them for many years. But we weren’t happy. Player characters were whiffing a lot and once they did hit they were one-shotting the enemy. Whenever an OSR module had 5e stats, like Temple of the Blood Moth, that always worked a lot better.
So for our visit to Arden Vul (at the time of writing, we’re forty sessions deep into that campaign), we switched back to Shinn’s version. It worked so much better!
Not having any XP values easily available was a problem, and my players are weird about expecting monsters to work similarly to PCs, so if they see someone fighting with 1d6+8, they think “that’s one hell of a magic weapon” and get suspicious when they pick it up and it’s not.
Looting isn’t the only or even the biggest issue. It happens often that they end up recruiting or even running characters that started as NPCs or enemies.
So in my table here, I worked with Stan Shinn’s table and with the table in the Forge of Foes book to find numbers where there is some plausible explanation for the new HP and damage values, and set appropriate XP. More HP is explained by high constitution and more hit dice, and more damage is more dice and more attacks instead of high static modifiers.
Shinn has different AC values at different levels. And inverted, to compensate for 1e’s steeper curve. So HD1 creatures would have 20-1e AC, HD2 would have 19-AC etc. That has worked OK. It gives values a lot lower than Forge of Foes, but that has been a good thing. But it’s a li’l fiddly. I changed that to 18 across the board, with the option of 21 for some armor types that the party is gonna loot.
One weird thing in the WotC monster manuals is that proficiency for monsters is based on their CR, not their HD, while (at least for the core MM), their spell slots and “caster levels” and such is based on the HD. Here I made the HD match up to proficiency bonus more consistently, both for monsters and people. Trying to have the best of both worlds of consistency and game play. The XP reflects the resulting CR.
