The Interpersonal Trust Short Scale—the English-language adaptation of the Kurzskala Interpersonelles Vertrauen (KUSIV3)—measures interpersonal trust as a psychological disposition with just three items (completion time ~ 30 s). The items of the German-language source version were translated into English using the TRAPD approach. Our empirical validation based on a heterogeneous quota sample in the UK shows that all the reliability coefficients of the English-language adaptation and its correlations with external variables are satisfactory and comparable to those of the German-language source version. Moreover, the results of measurement invariance testing suggest that metric measurement invariance of the scale holds when comparing the UK and Germany, implying the comparability of correlations based on the latent factors across the two nations. As an ultra-short scale, KUSIV3 lends itself to the assessment of interpersonal trust particularly in survey contexts in which assessment time or questionnaire space are limited. It is applicable in a variety of research disciplines, including psychology, sociology, and economics.