The dragons are getting bigger in season 7. To be honest, they do look bigger every year but in this season they are really huge. Game of Thrones director Matt Shakman tells EW:
“The dragons this year are the size of 747s. Drogon is the biggest of the bunch — his flame is 30-feet in diameter!”
For reference, a Boeing 747 is around 76 metres (250 feet) long with a wingspan of about 68 metres (224 feet).