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Most countries in the world now use the metric system. Almost the only holdout is the USA which, oddly enough, still uses the old British Imperial system of weights and measures. The only units the two systems have in common are time units from second to century.

We use "=" signs below, but all are approximate.

[edit] Temperature

	←freezing			cold		cool		warm		hot		swelter		cooked
°C	0	4	7	10	13	15	18	21	24	26	30	32	35	40
°F	32	40	45	50	55	60	65	70	75	80	85	90	95	104

100 °C — 212 °F — water boils 37 °C — 98.6 °F — human body temperature 0 °C — 32 °F — water freezes -18 °C — 0 °F — ouch -40 °C — -40 °F — forty below zero!

Humidity. Hot weather, say 80°F (26°C) and up, is more uncomfortable in humid air than in dry air because dry air allows more sweat to evaporate from your skin and this cools you but humid air inhibits this evaporation and leaves you more susceptible to overheating.

Drink lots of water in hot weather to replenish the water your body sweats as it attempts to cool itself.

A temperature drop will catch you by surprise one day without a jacket. Pack sufficient clothes to bundle up.

[edit] Length and distance

• 1 inch (1") = 2.54 cm
• 1 foot (1') = 30 cm
• 1 mile = 1.6 km

[edit] Comparisons

• A credit card is about 0.75 mm (3/4 of a millimetre) thick.

• 1 cm (centimetre) is the width of an average fingernail.

• 1 Km (Kilometre) takes about 15 minutes to walk.

[edit] Weight

• 1 kg = 2.2 pounds
• 1 ounce = 28.54 grams
• 1 pound = 454 grams

For China, the jing is almost exactly 500 grams.

[edit] Surface area

For small things, one might use square inches or square centimeters. There are about 6.5 cm² to one in².

For floor area of an apartment, there are about 11 square feet to the square meter.

For large areas, there are about 2.5 acres to the hectare.

[edit] Volume

The standard metric unit of volume is the liter. Many things, however, are measured in ml (milliliters) or equivalently in cc (cubic centimeters). Roughly, a teaspoon is 5 cc and a fluid ounce is 30 cc.

Beware, 1 US gallon = 2 US quarts = 8 US pints. 1 British gallon = 2 British quarts = 8 British pints. But the two are different, 1 US gallon = 3.78 litres, 1 British Gallon = 4.54 litres.

For car and motorcycle engines, displacement might be given in cc or liters or cubic inches. 1000 cc or one liter is 61 cubic inches.

[edit] Comparisons

• 1 litre of water weighs 1 Kg. Since many liquids (milk, orange juice) are sold in litre containers it is easy to judge 1 litre or 1 Kg.

• 1 litre is equivalent to a cube 10 cm x 10 cm x 10 cm.

• 1 Cubic Metre (1 m³) = 1000 litres. 1 m³ of water weighs 1000 Kg = 1 Tonne. Do not try to pick this up yourself!

• In Europe, wine is usually sold in 700 ml (0.7 litre) bottles (occasionally 750 ml or 1 litre).

[edit] Metric prefixes

1 mm = 1 / 1000 metres, 1 mg = 1 / 1000 g

1 cm = 1 / 100 metres.

1 Km = 1000 metres, 1 Kg = 1000 grammes.