Scaling BPM on the ranking criteria

The Ranking Criteria's rules and guidelines are based around songs of 180 BPM with 4/4 time signatures. This guide clarifies how that scaling works!

We'll be using the following osu! Normal difficulty guideline as an example:

Note density should consist of mostly 1/1, occasional 1/2, or slower rhythms.

For the sake of simplicity, think of 180 BPM as a midpoint.

• As a song's tempo goes from 180 BPM to ~120 BPM, guidelines become more lenient. For this example, increased frequency of 1/2 rhythm is generally okay to the point of almost constant 1/2 chains at 120 BPM.
• As a song's tempo falls below ~120 BPM, 1/4 rhythms can be slowly introduced. Closer to 120 BPM, that would mean very rare 1/4 rhythms in chains of 2 objects or so.
• As BPM lowers further, more 1/4 rhythms are acceptable until reaching 90 BPM, where double the density of existing guidelines apply.

This low BPM range could easily be equated to increasing tempo from the 180 BPM base.

• As a song's tempo rises from 180 BPM to ~240 BPM, less 1/2 rhythm is acceptable.
• Near 240 BPM, minimal 1/2 rhythm should be used.
• Beyond 240 BPM, no 1/2 rhythm should be used, just as maps above 120 BPM should avoid 1/4 rhythm.

For the most part, 120 BPM and 240 BPM act as breaking points for when a map's rhythm should be doubled and halved according to guidelines. As BPM approaches these values, rhythm should reflect that through changes in density. For the sake of this example guideline, it's best to assume that using 1/4 above 120 BPM or 1/2 above 240 BPM is not a good choice for a Normal difficulty.

The same general concept applies to other rhythm-related guidelines as well, such as the osu! Normal difficulty guideline, "Avoid more than three actively clicked 1/2 rhythms in a row." As BPM increases from 180 to 240, active 1/2 should be gradually removed and frequency of consecutive 1/2 sliders should go down. As BPM decreases from 180 to 120, active 1/2 can gradually increase as well as 1/2 slider usage.

While this guide is oriented around guidelines for osu! Normal difficulties, it also applies to other difficulties and game modes. For example, osu! Easy difficulties require 4 beats of recovery time after spinners according to the Ranking Criteria. At 180 BPM, that is true, however at 120 BPM, it would be fine to use 3 beats of recovery, and that could gradually shift to 2 beats at 90 BPM.