体脂肪率，又称体脂百分比、体脂率，是将脂肪含量用其占总体重的百分比的形式表示，一般用于动物，但近年开始有在人体的应用。对于动物来说，体脂百分比的计算法是把动物体重中的脂肪部分重量与整个身体的分量相除，再乘以100%，脂肪包含必需脂肪酸(essential fat)及保存脂肪(storage fat)。所谓必需脂肪，就是指身体要维持生命及繁殖所需的脂肪。一般而言，女性的必需脂肪比例会比男性为高，因为需要生育、喂哺及其他由荷尔蒙调节的身体机能。对于男性，必需脂肪一般占体重的2～5%，而女性约为10～13%。保存脂肪由脂肪组织内所累积的脂肪组成，当中部份位于胸腔及腹部，用以保护身体的内脏。一般来说，最小的建议总体脂百分比都会比身体的必需脂肪比例高。直接测量体脂百分比具有一定的难度，所以现时网上一般的方法，都是透过对人的性别及体重数据作出评估。

The body fat percentage (BFP) of a human or other living being is the total mass of fat divided by total body mass; body fat includes essential body fat and storage body fat. Essential body fat is necessary to maintain life and reproductive functions. The percentage of essential body fat for women is greater than that for men, due to the demands of childbearing and other hormonal functions. The percentage of essential fat is 3–5% in men, and 8–12% in women (referenced through NASM). Storage body fat consists of fat accumulation in adipose tissue, part of which protects internal organs in the chest and abdomen. The minimum recommended total body fat percentage exceeds the essential fat percentage value reported above. A number of methods are available for determining body fat percentage, such as measurement with calipers or through the use of bioelectrical impedance analysis.