UnitConversion.org is quite the resource to easily convert between different units of measurement. It has over 2100 units in 78 categories, which range from those that are common, such as, length, weight, volume, currency, velocity, and pressure, to more specialized categories like magnetic flux density, electrostatic capacitance, and surface tension.
123 mm = 12 stacked CD cases. 6 miles = 30 Eiffel Towers. 5 acres = 11 ice hockey rinks. Sensibleunits.com converts any length, area or mass into real objects.
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