Size
Most bottom-mount fridges sit in the 400-530L range, big enough to suit families of 4-6 people. At the smaller end of the spectrum, capacities range from roughly 200 to 400 litres – suitable for couples or anyone who needs an extra fridge for drinks.
Don't just look at the total capacity of the unit, but at how those litres of storage space are split between the fridge and freezer. Also, check if the fridge can fit in your kitchen and that you can open both doors without hitting any nearby cupboards.