While some conversion formulas force you to round up or down, they're close enough for reliable estimates. If you're cooking, for example, you probably won't ruin your cookies by being a single degree off. Unless you're a total perfectionist like Mrs. Fields, in which case you need to get yourself an oven with a more elaborate temperature dial.
Let's try another one. To convert from kilograms to pounds (approximately), multiply the number of kilograms by 2.2. To go the other way, divide the number of pounds by 2.2. Letting P represent pounds and K represent kilograms, we get the following formulas:
P = 2.2K
If The Merchant of Venice's Shylock wanted a pound of flesh, you could give him about 0.45 kilograms of flesh, and that would be the same thing. Hopefully it doesn't tick him off that you're using a different system of measurement. He doesn't seem like someone whose bad side you would want to be on.
A bread recipe from Germany says to add 0.5 kg of flour. How many pounds of flour is this?
When K = 0.5, P = 2.2(0.5) = 1.10. Therefore, 0.5 kg of flour is 1.1 pounds of flour. That's a lot of bread. We may need to pick up some more cold cuts.