Background Although the interest in Idiopathic Pulmonary Fibrosis (IPF) has increased in recent years due to the appearance of new therapies however the interest has focused on pulmonary involvement with little concern for systemic manifestations such as the nutritional status abnormalities. Thus, our study assessed the malnutrition prevalence in patients with IPF and the best indicators for the assessment of malnutrition among them. Patients and methods This work was conducted on 110 stable IPF patients who attended the outpatient clinic of Ain Shams University Hospitals from October 2020 to July 2021. Data about the detailed history and nutritional assessment was collected. Results 22.7% and 20.9% were malnourished according to the definition of fat-free mass index (FFMI) and body mass index (BMI), respectively. Most malnourished patients according to low FFMI were female; not using PPI was a significant independent predictors of malnutrition. There was a statistically significant relation between low FFMI and low serum albumin, hemoglobin, and oxygen saturation. Our findings also revealed that measuring BMI and being less than or equal to 22.1 kg/m2 and mid-arm circumference (MAC) less than or equal 28.5 cm is significantly related to low free fat mass index (malnutrition) and increases that risk by 31.63 folds. Conclusion Nearly one-quarter of IPF patients were malnourished and it was found that measuring BMI less than or equal to 22.1 kg/m2 together with MAC less than or equal to 28.5 cm can predict low FFMI and that can be used in our clinical approach.