Size isn’t everything with engines (there comes the point where they are too heavy), but engineering larger fans has led to improved performance. The Pratt & Whitney JT3D engines offered for the Boeing 707 for example have a fan diameter of just 130 centimeters. The largest engines today are over double this size.

GE9X – the biggest engine
The largest commercial jet engine offered to date is the General Electric GE9X engine. This has been designed for the new Boeing 777X. It is developed from the GE90 engine but has a larger fan and lighter construction. The GE9X holds the Guinness World Record for the highest recorded thrust, a huge 134,300 pounds. It is also 10% more fuel-efficient than its predecessor.

And for size, the front fan diameter is 340 centimeters. The total engine diameter is closer to four meters, making it wider than the fuselage of a Boeing 737. //

The Rolls-Royce Trent 900 was launched in 2003 for the A380. It is derived from (and is slightly larger than) the Trent 800 engine. It went on to be developed into the Trent 1000 for the Boeing 787, but this is a smaller engine.

The Trent 900 has a fan diameter of 295 centimeters. And it offers thrust of up to 81,000 pounds.