This dataset contains tabular files with durational measurements of vowels in connected speech. The data include measurements for 62 German learners of English and 25 native speakers of English (BrE and AmE). In total, 105 vocalic intervals were measured for each speaker, totaling 6509 measurements for learners (1 missing) and 2618 measurements for native speakers (7 missing). The data were elicited with a reading task, where participants read out short dialogues. The German subjects are instructional-setting learners ranging from grade 5 (age: 11) to university. They are predominantly from northern Bavaria and represent a broad range of proficiency levels. Pronunciation ability was assessed with a foreign accent rating.