Like every nation on Earth except Liberia, Myanmar and the United States, Japan uses the metric system. In the US, most of us are more comfortable with the antiquated and difficult British Imperial system we use. Honestly, the fact is that anyone who can add, subtract, multiply and divide by tens will have a very easy time with conversion the "metric way."
Weights
In the US, food and drinks are sold in pounds and ounces, grocers in Japan deal in grams, kilograms and liters for all measurements other than sake. A kilogram is equal to 2.2 U.S. pounds, and a gram is 1/1000th of this amount.
Temperature
Temperature in Japan, of course, is measured in Celsius. Here is a temperature conversion table for you.
Money
The standard of monetary exchange in Japan is the Japanese yen, approximately 0.00993345 US dollars, or $1USD = 100.670 Yen. It's an interesting thing to watch, the rise and mostly fall of the value of the US dollar, on international markets.
Here is a bit of historical piece... Shakkan-ho Although more complicated than the metric system, the old Japanese shakkan-ho standard of weights and measures - still used in the sake (rice wine) manufacturing industry - is remarkably consistent. The base unit is known as sho, which is the standard size for a bottle of sake - just short of two liters, which is roughly equivalent to half a gallon.
Traveling abroad and the metric systemWhen traveling abroad, it is important to understand the metric system and conversion factors related to what we encounter abroad. I've talked about a few things above, but have come up with some really helpful conversion factors everyone should know.
Helpful Conversion Factors
Ratio of an igloo's circumference to its diameter = Eskimo Pi
2000 pounds of Chinese soup = Won ton
1 millionth of a mouthwash = 1 microscope
Time between slipping on a peel and smacking the pavement = 1 bananosecond
Weight an evangelist carries with God = 1 billigram
Time it takes to sail 220 yards at 1 nautical mile per hour = Knotfurlong
Half of a large intestine = 1 semicolon
1,000,000 aches = 1 megahurtz
Basic unit of laryngitis =! 1 hoarsepower
453.6 graham crackers = 1 pound cake
1 million microphones = 1 megaphone
2 million bicycles = 2 megacycles
365.25 days = 1 unicycle
2000 mockingbirds = 2 kilomockingbirds
52 cards = 1 decacards
1 kilogram of falling figs = 1 Fig Newton
1 millionth of a fish = 1 microfiche