Interpersonal relevancy appraisals are a dynamic and understudied aspect of human social cognition. Despite their importance, there are no existing measures. This study developed and validated a new measure of self-perceived interpersonal threat, opportunity, and invisibility appraisals among a life-course sample of adults. We also explored the relationships between relevance appraisals, social connectedness, loneliness, age, and sex-assigned-at-birth. Items were developed based on a theoretical model of multi-domain interpersonal relevance appraisals and refined following feedback from five experts in social psychology. Cross-sectional data were obtained online from a sample of 1,079 adults (age 18-90 years), recruited from the general population of Australia. Data were split into two pseudo-random samples used for 1) scale development and evaluation, and 2) assessment of internal consistency, construct validity, convergent validity with social connectedness and loneliness, and exploratory analysis with age and sex. Results support the factor structure and internal consistency of 17- and 9-item versions of the Perceived Interpersonal Relevancy Scales (PIRS) and measurement invariance across younger and older age groups. Higher self-perceived threat and invisibility appraisals were associated with decreased social network size, increased loneliness, younger age, and male sex. Higher self-perceived opportunity appraisals were associated with increased social network size and decreased loneliness. Results support this new measure of perceived interpersonal relevance appraisals, which shows relationships between the way we believe others perceive us, loneliness, and social isolation. The PIRS likely has wide utility for studies that seek to understand the intersections between human social cognition, well-being, and health across the lifespan.