I realized that one thing missing from my post on converting Pathfinder modules to 5e was how to convert difficulties for skill checks and saving throws.

The Math

Pathfinder skill checks tend to scale much higher than in 5e. Between feats, magic that improves ability scores and skills, and the base skill ranks, a highly-focused Pathfinder character could conceivably hit DC 60 without too much difficulty by 20th level. A similarly-focused character in 5e will have expertise, an ability score capped at 20, and probably the use of advantage and some kind of bonus die (like bardic inspiration). The 5e character hits only DC 36 with a similar frequency to the Pathfinder character hitting 60.

Using the theoretically most-focused character from level 1-20 in both systems, as well as a hypothetical “good-but-not-amazing” character, I worked out the skill DC curve below in a way that seems to be equivalent throughout play.

Straight up ability checks that don’t involve skills (like Strength checks to force doors) are probably closer to a wash: A character in Pathfinder can get ability scores over 20, but can’t usually apply most of the other bonuses that scale really high. 5e characters have access to advantage, and most miscellaneous bonuses (like bardic inspiration) apply to straight ability checks as easily as to skill checks, even if a high-ability-score character in 5e will be a few points behind a similarly focused character in Pathfinder. And, honestly, these checks are relatively uncommon at mid-to-high level anyway (since you can use utility magic to bypass them), so will tend to come up most frequently when characters have a similar range of ability bonuses anyway.

Meanwhile, saving throws are easier to figure out, since 5e tends to construct them into a very standardized 8 + proficiency + ability bonus. This means that you can assume DCs are almost always going to range from 10-21, and can figure out the most appropriate one by just figuring out the effective level of the threat plus the intended challenge of the threat (really easy threats are just 8 + proficiency + 0, while really hard ones are 8 + proficiency + 5).

The Conversion

Skill DCs

Pathfinder DC 5e DC
10 8
15 12
20 17
25 20
30 22
35 24
40 27
45 29
50 32
55 34
60 36

For DCs under 20, just take off 2-3 points of DC. For DCs of 20+, half + 7 gets you really close to the curve.

Ability Check DCs

If the ability doesn’t take a skill bonus, just use the printed ability check DC.

Saving Throw DCs

Figure out the approximate CR of the threat (when in doubt, just use the average PC level). Set the DC to 8 + that CR’s proficiency bonus + 0-5 (depending on how serious the threat is supposed to be).

For very quick and dirty math, just set the DC to half the CR + 10 and adjust it up or down by a point or two based on how serious the threat is.