Guide
IPC vs CPC: The Key Differences
The IPC (International Patent Classification) and the CPC (Cooperative Patent Classification) organize the same universe of technology, but at different depths. The IPC is the global standard: WIPO maintains it, and patent offices in more than 100 countries print its codes on every published document. The CPC extends the IPC with roughly three times as many entries. The EPO and the USPTO built it for one job: finding prior art with precision.
Side by side
| IPC | CPC | |
|---|---|---|
| Maintained by | WIPO | EPO and USPTO jointly |
| Entries (2026.01 release) | 80,145 | 254,249 |
| In force since | 1975 | 2013 |
| Revision cycle | Once a year (January 1) | Several times a year |
| Sections | A–H | A–H plus Y |
| Typical use | Global baseline on every published patent document | Fine-grained prior-art search at EPO, USPTO and partner offices |
What both systems share
Both systems use the same five-level hierarchy: section, class, subclass, main group, subgroup. A code like H04L 9/32 means the same thing in both: verifying identity in secure communication. Because the CPC grew out of the IPC, every CPC code below the Y section slots into the IPC structure. Our guide to reading classification codes walks through the hierarchy level by level.
What the CPC adds
- Granularity. The CPC subdivides IPC groups into finer subgroups. Where the IPC stops, the CPC often continues two or three levels deeper. That is the difference between 80,145 and 254,249 entries in the current release.
- Section Y. The CPC-only section Y tags cross-cutting technologies. Its best-known class is Y02, which covers climate change mitigation. The IPC has no equivalent.
- 2000-series indexing codes. The CPC adds supplementary codes for aspects that the main classification does not capture.
- Faster revisions. WIPO revises the IPC once a year. The EPO and USPTO update the CPC several times a year, so new technology gets a precise code sooner.
What do "Not Allocatable" and "Additional Only" mean in the CPC?
Two conventions exist only in the CPC. A code marked Not Allocatable is a structural placeholder: it organizes the hierarchy, but examiners cannot classify a patent under it directly and must pick one of its children. A code marked Additional Only can never be the first classification of a document; it only captures auxiliary aspects next to the main code. Both flags appear on the CPC detail pages of this site.
Which one should you use?
- Reading a patent document: you will meet the IPC. It appears on every published application and grant worldwide.
- Searching prior art: prefer the CPC where available. Its finer subgroups narrow a search far more than the IPC can.
- Cross-office statistics: use the IPC. It is the only system every office applies.
See the difference for any code
The Diff view on this site compares both systems side by side for any code and highlights what the CPC adds, changes or drops. Two starting points: