Pollution of the world's oceans by marine debris has direct consequences for wildlife, with fragments of plastic <10 mm the most abundant buoyant litter in the ocean. Seabirds are susceptible to debris ingestion, commonly mistaking floating plastics for food. Studies have shown that half of petrel species regularly ingest anthropogenic waste. Despite the regularity of debris ingestion, no studies to date have quantified the dimensions of debris items ingested across petrel species ranging in size. We excised and measured 1694 rigid anthropogenic debris items from 348 petrel carcasses of 20 species. We found that although the size of items ingested by petrels scale positively with the size of the bird, 90% of all debris items ingested across species fall within a narrow “danger zone” range of 2–10 mm, overlapping with the most abundant oceanic debris size. We conclude that this globally profuse size range of marine plastics is an ingestion hazard to petrels.