The 40-item Fat Microaggressions Scale (FMS; Lindloff et al., 2024) assesses the frequency that fat people experience weight-related microaggressions, where microaggressions are brief, recurrent, commonplace acts that demean and discriminate against members of stigmatized groups. The FMS can be administered online or in-person to adolescents and adults who self-identify as fat, overweight, or higher-weight, and is free to use. This chapter first discusses the development of the FMS and then provides evidence of its psychometrics. More specifically, the FMS has a 4-factor structure within exploratory and confirmatory factor analyses: Direct Experiences (11 items), Indirect Experiences (12 items), Benevolent Weightism (11 items), and Clothing Exclusion (6 items). Internal consistency reliability, test-retest reliability, criterion-related, incremental, and known-groups validity support the use of the FMS. Next, this chapter provides the FMS items in their entirety, instructions for administration and scoring, and the item response scale. Logistics of use, such as permissions, copyright, and contact information, are available for readers.