The study compared the accuracy of ultrasound attenuation coefficient measurement (ACM) in the assessment of hepatic steatosis with magnetic resonance imaging (MRI-PDFF) and chemical analysis of fat. 60 multimodal fatty liver phantoms with different fat contents were examined. ACM showed a strong correlation with fat chemical analysis (r = 0.878, p < 0.001) and also with MRI-PDFF (r = 0.846, p < 0.001). The intra-observer reproducibility of the ACM was excellent (ICC = 0.956, p < 0.001). The diagnostic performance was high: the AUROC value was 0.984 for ACM and 0.996 for MRI-PDFF. The results confirmed that ACM is a reliable, accurate and cost-effective non-invasive method for the quantification of hepatic steatosis.