pacman -Qi $(pacman -Qu | cut -f1 -d' ') | grep -E '^Name|Installed Size' | grep -E '^Name|( [0-9]{2}(\.[0-9]+)?\s+MiB)'

Find the biggest packages that are about to be updated. (Actually, find the packages that need to be updated that are bigger than 10MiB on disk.)