The width is usually the first thing people compare when buying a desk. In a test room, it turned out to be the least important of three things.

Width is the smallest difference

105 × 50120 × 60Change
Width105 cm120 cm+14%
Depth50 cm60 cm+20%
Floor area0.525 m²0.720 m²+37.1%

Most of that 37% comes from depth. When a listing says "120 cm desk" and nothing else, go find the depth.

Pick by what sits on it

On the deskGetWhy
A laptop105 × 50Plenty of room for the laptop and your wrists
One 27-inch monitor120 × 60Many stands are close to 20 cm deep, which puts a 50 cm desk's screen right in your face
Two monitors120 or widerTwo screens side by side are a squeeze at 105
Books and paperEitherYou'll use the width for spreading out more than the depth

Where it goes matters more than either

Single bed110×200Large desk120×60Chair55×55DOOR 80310300
Desk in the middleA 310 × 300 cm room: single bed, 120 × 60 desk and chair.

In a 310 × 300 cm room, the big desk sat near the middle of the top wall, 30 cm from the bed on one side and 35 cm from the wall on the other. The planner found no route into the back of the room.

Swapping in the 105 × 50 desk in the same spot changed nothing. Both gaps were still under 60 cm.

Keeping the 120 cm desk and sliding it 35 cm into the corner, with the bed pushed into the opposite corner, opened an 80 cm gap and a clear route. You can open that version from the plan details box.

Save room for the chair

The planner draws a chair as a fixed 55 × 55 square, but a real one rolls back when you sit and again when you stand. Leaving about 70 cm clear on the chair side gets you close. If you draw the chair tucked under the desk you'll get a red overlap warning; the planner is flat and doesn't know the chair is shorter than the desktop.

Source

The 105 × 50 cm size matches the published IKEA MICKE desk (https://www.ikea.com/kr/ko/p/micke-desk-white-80354276/).