Converting difficulty class (DC) of checks from D&D 3E to 5E

Question

I'm looking at converting the 5th-level D&D 3E adventure The Speaker in Dreams to the fifth edition and I'm noticing a lot of DCs from 20 to 30. Were difficulty classes higher in 3E or were players able to consistently roll higher checks because of a specific mechanic compared to 5E? Should I be reducing the DCs of checks when converting, if so is there a good fixed value or formula to decrease the DCs by?

Examples:

The characters can scale the 25-foot-high town walls with a series of Climb checks (DC 30).

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A successful Gather Information check (DC 20) reveals the following information about the recent murders.

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If the party uses the same route into the warehouse (Climb DC 21), proceed with the following description.

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A locked chest (average lock, DC 25) kept underneath the stairs holds the treasure the grimlocks cannot easily use:

Answer 1

Were difficulty classes higher in 3E or were players able to consistently roll higher checks because of a specific mechanic compared to 5E?

Yes and yes. DCs were higher and the mechanics of the game allowed much higher bonuses. Mid-level characters would have +15 to +25 in the things they were good at and be completely useless in the things they weren’t.

One of the specific design goals of 5e was “bounded accuracy” to put a stop to all that.

Should I be reducing the DCs of checks when converting, if so is there a good fixed value or formula to decrease the DCs by?

Yes and sort of.

The 3e DC ranges are described here. The 5e ones are here. There’s no exact correspondence but if you look at the qualitative description in 3e and match them to 5e you’ll be close enough.

Answer 2

I'm afraid you can't just "convert" difficulty

Aside from higher DC limits, there are more significant differences between 3.x and 5 editions:

• There is no "using a skill" concept in 5e at all. There are only Ability Checks and the difference is substantial. 5th edition are pretty open regarding to ability checks now, leaving them as a tool for the DM. In 3E skill checks were rather mechanical players' tools with respective rules like Take 10/20, consistent outcomes, specific rules for retry, etc.
• 3.x "skill monkeys" are gone, so are typical scenarios when they were appropriate. In 5e you can't actually invest in a skill, instead there are proficiencies and expertise which work very differently, but 3.x adventures do not address this discrepancy in any way.
• 5e borrows several concepts from older editions, stepping aside from the pattern "you must succeed this particular check, then this one, then another one" for task resolution. Outcomes are often narrative-based. The game rewards players for a certain amount of ingenuity, cleverness, and cunning, even if their stats or roll results wasn't very great.

Let's look at a specific example:

The characters can scale the 25-foot-high town walls with a series of Climb checks (DC 30)

There is no way 5e characters can succeed a series of checks with DC 30, but the big number isn't the biggest problem. 5e adventures typically does not use "succeed a series of this specific checks" no more. Specific DCs are still a thing, but they are much more rare now. So changing this to something like "The characters can scale the 25-foot-high town walls with a series of Climb checks (DC 15)" still is not very 5e-ish.

Instead, the game expects players to describe, what do they actually do, then DM sets a difficulty class, then players roll dice, then DM describes the result. Or the same but without dice — DMG actually allows diceless task resolution (but not combat) as a legal way of playing, see p. 236.

So what can you do? My best bet is to use common sense and improvise. When players describe their actions, use the "Typical Difficulty Classes" from PHB page 174 before asking them to roll dice. DC from 3E might give you an idea about how hard this particular task is, giving you better understanding of a situation, but trying to directly convert 3E difficulty class to 5e mechanics wouldn't work well.

Answer 3

In the Player’s Handbook: Core Rulebook I v.3.5 on page 64 the Table 4–3: Difficulty Class Examples:

\begin{array}{lll} \textbf{Difficulty (DC)} & \textbf{Example (Skill Used)} \\ \hline \text{Very easy (0)} & \text{Notice something large in plain sight (Spot)} \\ \text{Easy (5)} & \text{Climb a knotted rope (Climb)} \\ \text{Average (10)} & \text{Hear an approaching guard (Listen)} \\ \text{Tough (15)} & \text{Rig a wagon wheel to fall off (Disable Device)} \\ \text{Challenging (20)} & \text{Swim in stormy waters (Swim)} \\ \text{Formidable (25)} & \text{Open an average lock (Open Lock)} \\ \text{Heroic (30)} & \text{Leap across a 30-foot chasm (Jump)} \\ \text{Nearly impossible (40)} & \text{Track a squad of orcs across hard ground after 24 hours of rainfall (Survival)} \\ \end{array}

Compare this table to the Typical Difficulty Classes table found in the fifth edition Player’s Handbook on page 174:

\begin{array}{lll} \textbf{Task Difficulty} & \textbf{DC} \\ \hline \text{Very easy} & \text{5} \\ \text{Easy} & \text{10} \\ \text{Medium} & \text{15} \\ \text{Hard} & \text{20} \\ \text{Very hard} & \text{25} \\ \text{Nearly impossible} & \text{30} \\ \end{array}

You can see the task difficulties of Very easy, Easy, and Nearly impossible exist in both. So a possible formula to convert from a third edition DC to fifth edition is:

If the 3E DC is between 0 and 5, just add 5 to create the equivalent 5E DC.

After the Easy task difficulty the labels don't match up again until Nearly impossible. We have the range of values in 3E from 5–40 that need to map onto the 5E range of 10–30. Therefore, each 5E DC will be 4/7 the equivalent 3E DC. Because the 3E DC will be greater than 5 we need to subtract 5 before multiplying by 4/7 and afterwards the 5E value needs to be greater than 10 so we'll add 10.

So if the 3E DC is greater than 5, a possible formula to convert to 5E DC would be:

5E DC = (3E DC - 5) * (4 / 7) + 10

In the question's examples the DC 30 Climb check would become:

(30 - 5) * (4 / 7) + 10 = ~24