在化学中，酸值（或称中和值、酸价、酸度）表示中和1克化学物质所需的氢氧化钾（KOH）的毫克数 。酸值是对化合物（例如脂肪酸）或混合物中游离羧酸基团数量的一个计量标准。典型的测量进程是，将一份份量已知的样品溶于有机溶剂，用浓度已知的氢氧化钾溶液滴定，并以酚酞溶液作为颜色指示剂。

酸值可做为油脂变质程度的指标。当油脂酸败，三酸甘油脂会分解时成脂肪酸及甘油，造成酸值的上升。因此酸值常作为评价食用油的标准，台湾曾出现因抽检油炸用油，发现酸值过高的情形。

在生物柴油老化时也会出现类似的现象，老化的原因可能是因为长时间的高温（酯的热分解）或接触到酸或碱（酯的水解）。

In chemistry, acid value (or "neutralization number" or "acid number" or "acidity") is the mass of potassium hydroxide (KOH) in milligrams that is required to neutralize one gram of chemical substance. The acid number is a measure of the amount of carboxylic acid groups in a chemical compound, such as a fatty acid, or in a mixture of compounds. In a typical procedure, a known amount of sample dissolved in organic solvent (often isopropanol), is titrated with a solution of potassium hydroxide(KOH) with known concentration and with phenolphthalein as a color indicator.