The 2015 Honda Civic uses a 13.2-gallon (approximately 50-liter) fuel tank in most trims, including both the sedan and coupe versions.
Tank size and what it means for driving
How to verify your vehicle’s exact capacity
Summary
In short, a 2015 Honda Civic typically has a 13.2-gallon (50-liter) gas tank across most trims, with the exact capacity being easily verifiable via the owner's manual or the vehicle’s information placard.