Introduction Many factors affect the required dose of warfarin, including body weight, which is mentioned only in a few studies. Our study was conducted using body mass index (BMI) to assess the requirements for warfarin dosing. Methods A retrospective study was conducted that included adults who used warfarin for more than three months, with at least two consecutive international ratio (INR) readings within the therapeutic range. Results Over 301 patients were included; the 20% higher dose of warfarin was required in obese patients than normal BMI and overweight patients (32.2 ± 15.2 vs. 27.4 ±17.3 and 26.8 ± 12.7; p=0.013, respectively). Conclusion Obese patients required a higher dose than other patients, which should be considered when initiating or adjusting the warfarin dose.