Cubic ton

A Cubic ton is a measure of volume (compare fluid ounce). It is no longer used in the United Kingdom but seems to be still in use in the USA, see "definitions" below.

Definitions

A mass-derived unit of volume must be defined by reference to the density of some material. In the case of the fluid ounce, this is water. For the cubic ton, the situation is more complex—there are different cubic tons for different materials.

The Reader's Digest Great Encyclopaedic Dictionary gives the following ton-derived volumes:

• Timber, 40 cubic feet
• Stone, 16 cubic feet
• Salt, 42 bushels
• Lime, 40 bushels
• Coke, 28 bushels
• Wheat, 20 bushels

Defining a cubic ton presents some difficulties because:

• It is uncertain whether the above figures are based on the long ton or the short ton
• Organic materials, such as timber, vary in density

The nearest thing to a standard cubic ton seems to be the "timber" cubic ton (40 cubic feet) which is used by freight transport operators in the USA, ref: [1] and [2]

Conversions

• 1 cubic ton (40 cubic feet) = 1.133 cubic metres
• 1 cubic metre = 0.883 cubic tons (35.32 cubic feet)

These are approximate conversions, based on a cubic ton of 40 cubic feet, and will be subject to rounding errors.

Cubic tonne

There are many entries on the internet for cubic tonne but it is an unofficial unit. Its use should be discouraged because it is not an SI unit and there is uncertainty about its definition. The SI does not use mass-derived units of volume and the SI unit of volume is the cubic metre.

The metric system formerly did use a mass-derived unit of volume, the litre, which was defined as the volume occupied by one kilogram of water. That definition is no longer used and the litre is now defined as one cubic decimetre, although traditionally both synonyms are recognized.

In view of this precedent it is possible that some metric countries may, in the past, have used a cubic tonne but it has never been officially used in the United Kingdom. No definition of the cubic tonne has been found but, if it were defined as the volume occupied by one tonne of water, then it would be almost identical to the cubic metre.

Use by the BBC

The British Broadcasting Corporation (BBC) has used the term cubic tonne on at least three occasions:

• In a television report on greenhouse gases
• In a television report on Silbury Hill
• In an internet article on an Alpine tunnel

The BBC's use of this unofficial unit caused some amusement in chatrooms, for example: [3] The BBC obviously realised its mistake because it later amended the internet article by changing cubic tonnes to cubic metres, [4]

See also

• Tun (unit)

Sources

• The Reader's Digest Great Encyclopaedic Dictionary, 1964