Metric and Imperial equivalents

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Most countries in the world now use the metric or SI system. The old British imperial system of weights and measures survives, in various forms, in the United States, United Kingdom, Canada, and Liberia, to greater or lesser extents and Myanmar still ploughs its own furrow, but in all these countries, except for the US, the metric system is widely understood. In the US, you'll find the metric system only used in scientific or military contexts, while in the UK and Canada, usage is more mixed. In scientific usage, the metric system is used exclusively in all countries of the world.

To get by in countries that use a different system than you're used to, it's helpful to know some rough equivalents. We use "=" signs below, but some are approximations.


A Celsius poem

Zero is freezing
10 is not
20 is warm
and 30 is hot

frigid freezing cold cool mild warm hot swelter cooked→
°C  -40 -18 -4 0 4 7 10 13 15 18 21 24 26 30 32 35 40
°F  -40 0 25 32 40 45 50 55 60 65 70 75 80 85 90 95 104


 100°C  =  212°F  =  Water boils
  58°C  =  136°F  =  Highest temperature recorded on Earth
  37°C  =   98.6°F =  Human body temperature
  20°C  =   68°F  =  Room temperature
   0°C  =   32°F  =  Water freezes
 -18°C  =    0°F  =  
 -40°C  =  -40°F  =  Forty below zero!
 -89°C  = -129°F  =  Lowest temperature recorded on earth
-273°C  = -459°F  =  Absolute zero

To convert Metric (Celsius) to Fahrenheit, double the number and add 30. To convert Fahrenheit to Celsius, subtract 30 and divide in half. Close enough for our purpose. For science use



Length and distance[edit]

  • 1 inch (1") = 2.54cm
  • 1 foot (1') = 30.48cm
  • 1 mile = 1.609344km


  • A credit card is about 0.75mm (3/4 of a millimetre) thick
  • 1cm (centimetre) is the width of an average fingernail.
  • Most adults are between 1.5 and 2 metres tall.
  • 1 km (kilometre) takes about 15 minutes to walk.


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

For China, the jin (斤) is almost exactly 500 grams. In Germany the pound (Pfund) nowadays refers to a weight of exactly 500g.

Surface area[edit]

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

For floor area of an apartment, there are about 11 square feet in one square meter.

For large areas, there are about 2.5 acres in one hectare.


The standard metric unit of volume is the litre.

Many things, however, are measured in mL (millilitres) or equivalently in cc (cubic centimetres). Roughly, a teaspoon is 5mL and a fluid ounce is 30mL.

In both the US and Imperial systems, 4 quarts = 1 gallon and 2 pints = 1 quart. However, the US units are smaller than Imperial counterparts. A US quart is 32 fluid ounces while Imperial is 40; a litre is in between at 35. A US gallon is 128 ounces or 3.78 litres, while an Imperial gallon is 160 ounces or 4.54 litres.

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


  • 1L of water weighs 1kg. Since many liquids (milk, orange juice) are sold in litre containers it is easy to judge 1L or 1kg.
  • 1L is equivalent to a cube 10cm x 10cm x 10cm.
  • 1 Cubic m (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 750mL (0.75L) bottles (occasionally 700mL or 1L).

Metric units[edit]

1mm = 1/1000th metre

1mg = 1/1000th g

1mL = 1/1000th litre

1cm = 1/100th metre

1km = 1000 metres

1kg = 1000 grams

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