An order of magnitude is a difference between two numbers equal to multiplying one of them by ten. Orders of magnitude are quite easily and commonly described through the use of scientific notation and powers of ten.
One way of categorising things in the physical world is by their size. The pages below contain lists of items that are of the same order of magnitude in length, area, volume, or mass. This is useful for getting an intuitive sense of the comparative size of things and the overall scale of the universe.
In the following table the different quantities are lined up so that the following are in the same row: length and the time taken by light to cross that length, area of a square and the length of one side, volume of a cubes and the area of one face, mass of some water and its volume.
Units used in the table:
- Time: femtosecond (fs), nanosecond (ns), microsecond, (μs), millisecond (ms), second (m), hour (hr), day (dy), year (yr)
- Length: nanometre (nm), micrometre (μm), millimetre (mm), centimetre (cm), metre (m), kilometre (km), astronomical unit (AU), light year (LY)
- Area: square metre (m2), hectare (ha), square kilometre (km2)
- Mass: gram (g), kilogram (kg), tonne (t)
- Volume: millilitre (ml), litre (l), cubic metre (m3)
- Energy: electronvolt (eV), Joule (J)