The aim of the study is to present biometrical data of the fetal lung measured in real-time sonography in mid-pregnancy. In 313 healthy fetuses of singleton pregnancies between the 15th and 30th week of gestation the fetal lung was measured in the horizontal, sagittal and frontal cross-sectional planes. In each plane the lung was measured in the following levels: clavicula, heart at the atrioventricular level (four chamber view) and diaphragm, as well as the lung length. During observation time all parameters showed a significant linear increase (r2 > 0.9; p < 0.001). Furthermore we found a high correlation between the same lung measurements collected in the different planes. The intraobserver variability was 3-8%. Such references of different planes could be helpful for differentiation of a small (hypoplasia) or a large lung (malformation).