Most "standard" ATX cases tend to be around 40-44 cm tall (wide, if flipped sideways), 40-44 cm deep, and around 17-20 cm wide (or height if flipped sideways).
I think finding a case with 18 cm width or less (or 18 cm height in your case) would probably be the more challenging part. But generally speaking, the cheapo cases tend to be the ones with 18 cm width, as their manufacturer ddn't want to "waste" precious thin steel metal. 🤣
If you don't have a tape measure with you but you do spot a case that you like, one easier way to tell if the case is around 18 cm wide is to look at the slots for the 5.25" external (optical) drives. If there's almost no case bezel around the slot (i.e. about the thickness of your index finger on each side or less), then it's likely to be a "slimmer" ATX case 18 cm or less. And if the bezel appears to be slightly thicker (about 1.5 to 2x the width of your index finger on each side), then it's probably 20 cm or more. Simple as that.

momaka wrote on 2025-03-13, 10:54:

Most "standard" ATX cases tend to be around 40-44 cm tall (wide, if flipped sideways), 40-44 cm deep, and around 17-20 cm wide (or height if flipped sideways).
I think finding a case with 18 cm width or less (or 18 cm height in your case) would probably be the more challenging part. But generally speaking, the cheapo cases tend to be the ones with 18 cm width, as their manufacturer ddn't want to "waste" precious thin steel metal. 🤣
If you don't have a tape measure with you but you do spot a case that you like, one easier way to tell if the case is around 18 cm wide is to look at the slots for the 5.25" external (optical) drives. If there's almost no case bezel around the slot (i.e. about the thickness of your index finger on each side or less), then it's likely to be a "slimmer" ATX case 18 cm or less. And if the bezel appears to be slightly thicker (about 1.5 to 2x the width of your index finger on each side), then it's probably 20 cm or more. Simple as that.

thank you!