The easiest way is to learn the numbers 30°F, 50°F, 70°F and 90°F which equal the European numbers 0°C, 10°C, 20°C and 30°C. This way is almost correct, but the most accurate way of calculating it is to draw 32 degrees of the original number and multiply the answer with five and then divide it with nine, but this is nothing that can easily be calculated in the head, so I would reccoment you to use the first method.
Is simple to find out if you have a calculator near you. If you want to find out how many grams some ounces are, then you can just multiply the number with 28,35 to get the answer. The other way around you would have to multiply the pounds(16 ounces) with 0,545 to get the number of kilograms.
If you dont have a calculator, you can simply follow the table given:
|U.S. Measurements ||Metric Measurements |
|1/2 ounce||14 grams|
|1 ounce||29 grams|
|1 1/2 ounces||43 grams|
|16 ounces (1 pound)||454 grams|