Both “ton” and “tonne” are units of weight, but a “ton” is a British and American measure, while a “tonne” is a metric measure.
A “tonne” is equal to 1,000 kg. In the US it may be referred to as a “metric ton”.
You should be careful when using the word “ton”, as there are two different types – British and American.
The British ton (also used in other countries that have the Imperial system of weights and measures) is equal to 2,240 pounds or 1,016.047 kg. It is sometimes referred to as the “long ton”, “weight ton” or “gross ton”.
The North American ton (only used in the United States and Canada) is equal to 2,000 pounds or 907.1847 kg. It is sometimes referred to as the “short ton” or “net ton”.
The difference dates from the 19th century when the British adapted their existing system (the avoirdupois system) to create the more easily convertible Imperial system. The Americans continued to use the old avoirdupois units. This also explains why there are differences between other British and American measures, most notably pints and gallons – and why the Brits measure their body weight in stone while the Americans use pounds.
The different measures have specific applications in particular fields of industry, commerce or shipping.
If you need any further information, Wikipedia is a good source.