Telomeres are crucial biomarkers of cellular aging and health, providing insights into various physiological and pathological processes. Large variety of methods are described for telomere length measurements, each with their own advantages and disadvantages. This chapter explains a quantitative polymerase chain reaction (qPCR)-based method for measuring telomere length in peripheral blood mononuclear cells (PBMCs), with special focus on ways to limit variability between qPCR run and improve comparability of telomere length values. With methodology of relative and absolute quantification, troubleshooting tips, and other guidelines, this chapter serves as a resource for researchers to benefit from this cost-effective and high-throughput assay.