It depends on what site you use for...

I'm partially disagree with you:
1. I don't use sites, I buy directly from shops.
2. Common study of case: drywall
4x8 compared with 1219.2mm x 2438.4mm
or
4x12 compared with 1219.2mm x 3657.6mm
You have to memorize 12 digits in place of 2 or 3.
More than that you will find exposed something like this: 1.2m x 2.4m or 1.2m x 3.7m and when you went home you realize is too much or not enough.
3. The same things happening with furniture.