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Bigger or Smaller?

When you change the units, do the numbers get bigger or smaller?

Choose Your Units

Age 14 to 16
Challenge Level



Some units are particularly well suited to a given measurement because they turn out to give a small, whole number of units. Understanding this concept gives you a feel for the order of magnitude of the quantities.

What units would you measure these quantities in to make an approximation which was a reasonably small whole number?

  • The volume of a bacterium
  • The mass of an oak tree
  • The area of a leaf
  • The half-life of Uranium-235
  • The area of a football pitch
  • The average lifespan of a human
  • The volume of a bath tub
Can you reverse the process? For the following units, what physical phenomena might naturally be measured to be around 1 unit?


  • Millimetre
  • Newton
  • Angstrom
  • Joule
  • Volt
  • Microgram
  • Micrometre
  • Hertz
  • Parsec



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