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Tonne or Ton?

I just came across the problem of whether to use ‘tonne’ or ‘ton’ in a text, so I did a little research and came to the following conclusion. This conclusion, however, is not so simple – so, first of all, let’s look at the technical definition:
In the UK, the ton used to refer to a weight of 2,240 lbs, or 1,016 kg. However, in 1985 Britain went metric and the ton was discontinued in favour of the metric tonne, which is 1,000 kg. In the US, the ton is still used, but means 2,000 lbs, or 907 kg. America is one of the few places left that doesn’t use the metric system.

But which one do we use in writing – tonne or ton?

We can say, “We had a ton of fun at the weekend!”, but of course we are not talking about weight at all, so ‘ton’ is appropriate.

We can say, “Damn, this suitcase weighs a ton!”, and we are talking about weight, but we are exaggerating just a bit – so ‘ton’ is again good. The same applies when we talk about a twenty-ton truck, a 300-ton excavator, or a 300-ton aircraft – we are not being precise, we are just trying to give an idea of size.

So, what about containerisation? Surely we have some kind of standards here? Well yes, and then again, no. Containers come in five common standard lengths, 20-ft (6.1 m), 40-ft (12.2 m), 45-ft (13.7 m), 48-ft (14.6 m), and 53-ft (16.2 m). Typically they are 8 ft wide and 8ft high. As you see, the sizes are actually imperial, not metric. Container capacity is expressed in twenty-foot equivalent units (TEU, or sometimes teu), and relates to a 20 ft long x 8 ft wide container. Height is not so important, as deck space and weight are the key measures. Click HERE to go to Ports and Terminals.com for masses of information and vocabulary.

So what about their weight? The maximum gross weight for a 20 ft dry cargo container is 24,000 kg, or 24 tonnes (metric), but for a 40-ft container it is 30,480 kg, or exactly 30 tons (US).  So here you can see that for loading cargo onto ships, planes or trucks, it is very important which kind of ton or tonne we are talking about. It is also critical that buildings and structures have their stress and load factors calculated properly. However, engineers get around this sticky problem by talking about weight in pounds (lbs) in the US, and kilograms (kgs) in the rest of the world, so there shouldn’t be any confusion 😉

However, in normal writings for non-engineering types, it would be unusual to use such big numbers. I would write that my car weighs one and a half tons, not 1,535 kg, because I am not being precise. However, on the registration document the weight is quoted precisely as 1,535 kg, because here it matters. Americans, however, often use large numbers of pounds (lbs) when writing about impressively large machines, for example.

Confused? No need – if you want to give a general idea about weight, the word ‘ton’ is fine. If you want to be precise, use the word ‘tonne’, or even ‘metric tonne’ – or use exact kilogram equivalents.

2 Comments (+add yours?)

  1. coute
    Oct 05, 2014 @ 00:47:55

    Sigh, I’m doing research for a presentation and I have a need to convert something that I read in a text as being “4 tons” to kilograms but I don’t know which “ton” the writer meant. Since it’s for a college paper, I don’t just want to guess.

    Reply

    • Malcolm Pemberton
      Oct 08, 2014 @ 00:30:11

      Well, this is tricky, but depends first on where the writer lives. If it’s a metric country, 4 tons means 4 tonnes, or 4,000 kg in engineers’ language. Where is the research based?

      Reply

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