Abstract Background Calf Circumference (CC) is recommended by the European Working Group on Sarcopenia in Older People (EWGSOP) as part of the sarcopenia assessment algorithm. Clinicians’ are concern about accuracy of use in patients with high Body Mass Index (BMI) 25- 40 kg/m2 and low BMI < 18.5 kg/m2. The aims of this study are to: (1) Compare prevalence of sarcopenia using Raw and BMI adjusted CC measures and (2) Examine CC association with gait speed and Clinical Frailty Score (CFS). Methods An observational study of over 65 years in rehabilitation setting. All data collected as part of routine physiotherapy care. Premorbid CFS recorded and Gait speed (m/s) over 6meters calculated. The fattest part of the calf was measured to give Raw CC corrected to the nearest centimetres (cm). Raw CC measures of patients with BMI < 18.5, 25–29, 30–39 and ≥ 40 kg/m2 were adjusted for by adding 4 cm, subtracting 3, 7,12 cm respectively (Gonzalez et al, 2021) to give Adjusted CC. Cut off values for sarcopenia by gender as recommended by EWGSOP. Data was analysed using Pearson’ correlation and t- test. Significant values set at p ≤ 0.05 and r = 1. Results n = 99, 54% female. Low BMI and high BMI was 13% and 37% respectively with mean CFS of 5.4. Walking speed was slow, mean = 0.21 m/s. Moderate positive correlation observed between Raw and Adjusted CC measures (r = 0.713, p = 0.0001). Sarcopenia prevalence was 30% using Raw CC compared to 54% with Adjusted CC (p < 0.004). Weak association recorded for CC measures with gait- speed and with CFS; (r = 0.124 and 0.123). No significant difference in Raw and Adjusted CC measures in Frail (5,6,7) and Non- frail (1,2,3,4) groups; [33.9(4.8) vs 32.3(4.16)]; p = 0.26 and [34.1(5.7) vs 32.4(4.6)]; p = 0.07. Conclusion Sarcopenia prevalence was higher with Adjusted CC. Clinicians’ awareness of impact of BMI on calf circumference is important in sarcopenia screening.