Cancer-Related Fatigue (CRF), subjective symptom, is considered the most prevalent and disabling in cancer. To help caregivers better understand it, we developed and evaluated the psychometric properties of a visual analog scale to assess daily CRF. In our qualitative study, we conducted interviews with caregivers, patients and scientists (N = 30) to generate items and select the scale's format. We then administered the final scale to a sample of 104 patients hospitalized for cancer surgery. In our quantitative study, we evaluated psychometric items with standardized questionnaires to compare and identify the construct validity of our fatigue scale. Because clinicians need a cutoff to diagnose fatigue in daily care, we also analyzed the scale's sensitivity. Correlations evidenced good construct validity for our scale, with r = 0.886 (p > 0.01), confirming that both physical fatigue and psychological fatigue (r = 0.768) were effectively measured. The Receiver Operating Curve (ROC) showed good sensitivity and specificity (>0.80), giving clinicians a threshold to identify tired patients, with only a 3% chance of misdiagnosis. The Daily Fatigue Cancer Scale is a good tool to detect patient fatigue and improve patient care.