We introduce a dataset of time-aligned phonetic transcriptions focusing on vowel length (quantity) in Icelandic. Ultimately, this aims to support computer assisted pronunciation training (CAPT) software, to automatically assess length and possible errors in Icelandic learners’ pronunciations. The dataset contains a range of long and short vowel targets, including the first acoustic description of quantity in non-native Icelandic. Evaluations assess how manual annotations and automatic forced alignment characterise quantity contrasts. Initial analyses also imply partial acquisition of phonologically conditioned quantity alternations by non-native speakers.