The mileage or fuel efficiency of a KTM Duke 125 can vary depending on several factors, including riding conditions, riding style, maintenance, and terrain. As an estimate, the KTM Duke 125 typically offers a mileage of around 35-45 kilometers per liter (km/l) or approximately 82-105 miles per gallon (mpg). However, it's important to note that these figures can vary and should be considered as rough estimates. Actual mileage may vary based on the factors mentioned above and individual riding habits. It's always a good idea to refer to the manufacturer's specifications or consult with KTM dealers for more accurate and detailed information regarding the specific model and its fuel efficiency.