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Neonates and infants are more susceptible to lung diseases influenced by age. Spirometry measures lung volume changes to diagnose and monitor respiratory conditions. Children experience significant lung development. Reference values for tidal volume, especially in neonates, are limited in countries like Nepal due to a shortage of trained personnel and the scarcity of advanced spirometers. This study examines tidal breathing pulmonary function in neonates under six weeks and its determinants.A cross-sectional study was conducted at a tertiary hospital in southwestern Nepal from January 1 to December 31, 2023. Various factors related to babies and mothers in post-natal wards and NICU were documented. Infant pulmonary function testing, specifically tidal volume measurement, was performed on infants less than six weeks old.A total of 866 babies were included; 55.3% (n=479) were male. Most were term (84.9%), with 15.1% preterm (n=131). The mean birth weight was 2773 ± 302 g.The mean tidal volume (VT) in this study was 19.25 ml, and the volume per kilogram (VT/kg) was 7.08 ml/kg. No significant differences in VT ml (p=0.34) or VT ml/kg (p=0.89) were observed by sex or delivery mode. Infants weighing 2500 grams or more had significantly higher tidal volumes (p=0.02) and volumes per unit weight (p=0.045) than those under 2500 grams. No maternal factors—such as sleep duration, folic acid intake, smoking, diet, primiparity, hypertension, religion, or oligohydramnios—affected VT ml or VT ml/kg. However, significant differences were seen in VT ml and VT ml/kg among mothers with adequate iron and calcium intake during pregnancy.This study aims to provide baseline data on tidal volumes for Nepalese infants, which will inform further studies. Birth weight and gestational age were significant neonatal factors influencing tidal volume. Iron and calcium intake by mothers during pregnancy had a significant influence on the development of higher tidal volumes in babies.