Objectives: Evaluation of physical functioning is central to patient recovery from critical illness - it may enable the ability to determine recovery trajectories, evaluate rehabilitation efficacy, and predict individuals at highest risk of ongoing disability. The Physical Function in ICU Test-scored is one of four recommended physical functioning tools for use within the ICU; however, its utility outside the ICU is poorly understood. The De Morton Mobility Index is a common geriatric mobility tool, which has had limited evaluation in the ICU population. For the field to be able to track physical functioning recovery, we need a measurement tool that can be used in the ICU and post-ICU setting to accurately measure physical recovery. Therefore, this study sought to: 1) examine the clinimetric properties of two measures (Physical Function in ICU Test-scored and De Morton Mobility Index) and 2) transform these measures into a single measure for use across the acute care continuum. Design: Clinimetric analysis. Setting: Multicenter study across four hospitals in three countries (Australia, Singapore, and Brazil). Patients: One hundred fifty-one ICU patients. Interventions: None. Measurements and Main Results: Physical function tests (Physical Function in ICU Test-scored and De Morton Mobility Index) were assessed at ICU awakening, ICU, and hospital discharge. A significant floor effect was observed for the De Morton Mobility Index at awakening (23%) and minimal ceiling effects across all time points (5-12%). Minimal floor effects were observed for the Physical Function in ICU Test-scored across all time points (1-7%) and a significant ceiling effect for Physical Function in ICU Test-scored at hospital discharge (27%). Both measures had strong concurrent validity, responsiveness, and were predictive of home discharge. A new measure was developed using Rasch analytical principles, which involves 10 items (scored out of 19) with minimal floor/ceiling effects. Conclusions: Limitations exist for Physical Function in ICU Test-scored and De Morton Mobility Index when used in isolation. A new single measure was developed for use across the acute care continuum.