The "unit effect", as it's called, says that even if you're aware of the units in a measurement, your mind will still put more emphasis on the size of a number, rather than the value it carries:
Consumers will readily attach weight to completely fictitious product statistics, preferring items with the most bogomips, even if they have no idea of what the significance of that figure is. That may be disappointing, but apparently it's even worse than that-even when they do know what the units are, people tend to prefer a bigger number. As a newly released study shows, people would rather pay for expedited service to get things in 31 days than they would to get it in one month.
Of course its counter-intuitive, but if you aren't actively converting that measurement to other units, you aren't aware of your biases. Of course, as soon as you become aware of these biases, the unit effect goes away—so the next time you're told something will, say, ship in 31 days, do a quick check in your brain to see if that fits another familiar unit that casts a different light on the result.