Background: Muscle-specific strength (MSS), defined as muscle strength relative to muscle mass, is a key indicator in the assessment of sarcopenia and functional status, especially in patients with cancer. Dual-energy X-ray absorptiometry (DXA) is the reference method for estimating muscle mass, but its limited accessibility hinders routine use. This study aimed to evaluate the correlation between DXA-based MSS and MSS estimated through more accessible techniques. Methods: A cross-sectional study was conducted in 205 adult oncology outpatients. Muscle strength was assessed by handgrip dynamometry, and muscle mass was estimated using DXA, bioimpedance (BIA), ultrasound, and anthropometry. MSS was calculated by dividing grip strength by each muscle mass parameter. Results: MSS calculated with BIA, body weight, and calf circumference showed very strong correlations with MSS-DXA (r > 0.90). Ultrasound-derived MSS showed only a moderate correlation (r = 0.55; p < 0.01). Similar patterns were observed in both men and women. Conclusions: BIA and anthropometric methods, particularly those using body weight and calf circumference, are reliable and accessible alternatives to DXA for estimating MSS in oncology patients. These tools may help improve the identification and monitoring of sarcopenia in clinical settings with limited resources.