Lead protective garments worn by medical staff in the presence of x-rays develop defects over time. This work proposes a novel method of assessing the protective efficacy of the garments as defects develop. The proposed method applies updated radiobiology data from ICRP 103. This work applied the as low as reasonably achievable principle to devise a formula through which a maximum allowed defect area in lead protective garments can be calculated. This formula depends on the cross-sectional areas () and ICRP 103 tissue weighting factors () of the most radiosensitive and overlapping organs protected by the garment, the maximum allowed additional effective dose to the garment wearer due to the defects (), and the unattenuated absorbed dose at the surface of the garment (). The maximum allowed defect areas are separated into three regions: above the waist, below the waist, and thyroid. To be conservative, it was assumed that = 50 mGy yr−1, and = 0.3 mSv yr−1. Also conservatively, transmission was assumed to be 0%, as employing a non-zero transmission factor would increase the maximum allowed defect area. Maximum allowed defect areas were as follows: 370 mm2 for above the waist, 37 mm2 for below the waist, and 279 mm2 for the thyroid. These values can be compared to commonly published values which are 670 mm2 for an apron, 15 mm2 over the gonads, and 11–20 mm2 for the thyroid. The proposed method for lead protective garment assessment is highly adaptable as values can be adjusted as radiobiology data are updated, and as values such as radiation dose limits vary across jurisdictions. Future works will include collection of data for unattenuated dose to apron () as it varies across professions, so that garments may be allowed different defect areas if relegated to individuals of specific professions.