# How to correctly express volume units

I have to replace imperial units with metric units in a text, and since this is not technical writing , I have to maintain the prose style and clarity.

This is a troubling phrase: "...the air in 1 cubic foot...".

I think I can do that: "...the air in a 30-centimeter cubic region [or cubic volume]...", but since I've seen units being used wrongly before (like saying that 1 cubic foot = 30 cubic centimenters), I would like to have your opinion on this.

BTW: I'm not a native English speaker, nor have I used imperial units daily (my country uses metric).

EDIT: I can't use liters because this is describing a cubic area of space, and 30 liters (or 28 liters) is hard to picture as cube. Take a look at it on another way. When I say "this is a two-feet cubic volume", how big do you think it is in cubic feet?

Also, did you understand the diference between saying "X-feet cubic volume" and "Y cubic feet"?

EDIT2: Here is a new doubt, what is the more correct way of writing this: "the space of a 30-centimeter cube" or "the space of a 30 centimeter cube" (the difference in the hyphen).

• `(like saying that 1 cubic foot = 30 cubic centimenters)` You're right, that is incorrect. 1 cubic foot is equal to 28,316.8466 cubic centimeters. – Phoenix Dec 16 '11 at 22:41
• @Theta30 not really, my doubt here is: if I say "X-centimeter cubic volume/region", is it understood as a cubic volume/region with sides of length X-centimeter? Also, is the way I suggested me most adequate way of adapting this text, or, is there a more "proseable" way of saying that? – Luiz Borges Dec 16 '11 at 22:50
• Can you provide more of the surrounding context? Is this a conversational context (e.g. dialogue)? – Jonathan Van Matre Dec 17 '11 at 1:46

If the context shows that "the air in 1 cubic foot" is specifically a cube-shaped volume of air, I would translate it as "the air in a 30-centimeter cube" (or, if greater precision is warranted, a 30.5-centimeter cube or a 30.48-centimeter cube).

If "the air in 1 cubic foot" is simply identifying the size of the volume rather than its shape, I would translate it as "28 liters of air". If 28 seems too precise, you can round it to 30, which overstates the size of a cubic foot by less than 6%.

If you think, as you seem to, that visualizing a cube of the correct size is important, then obviously go with the first option. A 30-centimeter cube is less than 5% smaller than a one-foot cube, so unless high precision is necessary, it's probably a good translation.

• The usage I want is indeed the first one, but I think the work cubic is the source of confusion here. The reply by Brian Nixon using the word cube instead seem to make it clearer. – Luiz Borges Dec 17 '11 at 0:40

If your country uses metric units, you may find that converting the measure to metric would be adequate. One cubic foot is roughly 30 X 30 X 30 cubic centimetres, or of the order of 27 litres.

In Britain it is customary to convert metric measures into more readily understood units; the height or length of a double-decker bus is a favourite, or the area of a football pitch, or the height of Nelson's Column.

27 litres presents a bit of a difficulty; it is too big for a bucketful but not large enough for a barrel.

• See my last edit. – Luiz Borges Dec 16 '11 at 23:16
• @LuizBorges, I quite understand the difficulty; one cubic foot is just inconvenient in that there is nothing in daily use that is about that size. A two-feet cubic volume would be eight cubic feet, which is rather too large. – Brian Hooper Dec 16 '11 at 23:26
• I used the two-feet cubic volume to show how a small change in word order can create a big change. In my case, I think that the "30-centimeter cubic volume" is a good adaptation of the "1 foot cubic". I just don't know it is clear enough that I'm talking about a cube with 30x30x30 cm and if there is a better way of saying that (still using lenght measures). – Luiz Borges Dec 16 '11 at 23:33
• @Luiz: To me, "30 cm cubic volume" seems rather confusing (and I suspect it may even be grammatically incorrect) as it seems to mix a measure of length with a measure of volume. To adapt Brian's suggestion, I would say a "30x30x30 cm volume" would be much better. But is there any reason why you cannot use "the air in "28.3 dm3" or "28.3 cubic decimetres"? Would this be too technical for you intended audience? Perhaps you could say something like "the volume of air in a 30x30x30 cm cardboard box (or container)" to make it easier to visualize? – Bjorn Dec 16 '11 at 23:47
• Brian, isn't 27 litres " a week's worth of beer"? – Tim Lymington Dec 17 '11 at 14:55

The distinction I think you’re trying to make between x-feet cubic volume” and y cubic feet” (where if x is 2 then y is 2³=8) doesn’t read well. I suggest it might be better written as “the volume of an x-foot cube”.

This answer covers the use of the hyphen and the singular, though there’s no hard-and-fast rule on hyphenation (as you’ll see if you search this site for “hyphen”; start, for example, with these questions:   ).

• Hum... I think that "the space of 30-centimeter cube" sounds less confusing than "a 30-centimeter cubic space". – Luiz Borges Dec 17 '11 at 0:33
• Should I use an hyphen between X and the unit? (30-centimeter vs 30 centimeters). Are these equivalent? Which way is more correct and which requires a plural? – Luiz Borges Dec 17 '11 at 0:44
• @LuizBorges I suppose there are other questions here that deal with "30-centimeter" vs. "30 centimeters", but I'll give a quick rule of thumb: if the phrase modifies a noun, use a hyphen and singular. Otherwise, don't use a hyphen, and use the plural if the number is greater than one. This usage varies somewhat, however, geographically. And as you may know, outside the USA, the correct spelling is "centimetre". – phoog Dec 20 '11 at 17:47

You could try "the air in a cube, 30 cm on each side".

This isn't really about metric/imperial. OP mentions "a two-feet cubic volume", which is not acceptable usage.

When we speak of volumes, we do so in linear measurements. It's more or less okay to speak of, say, 25 cubic foot - but most people would round it up and say almost a cubic yard. Metric or imperial - use the nearest familiar "rounded" linear measure that gives the right value when cubed.

It's not clear to me whether OP needs to convey the volume or the size/shape. For simple volume, "30 litres" is best. To describe (an object's) size/shape, I would say "a cube 30cm on the side".

• If you look at my question, I only brought the metric/imperial subject to explain what I was doing, the title of my question is "How to correctly express volume units". So far it has be refined to be: saying "10-foot cube" is correct usage to mean a "cube of lenght 10 foot on the sides"? BTW: The nearest familiar "rounded" linear measure for a "1 foot cube" in metric is a "30 centimeter cube", the other options are the technical 0,3 meter cube or the unfamiliar 3 decimeter cube. – Luiz Borges Dec 17 '11 at 1:29
• Oh, and if you mean to use cubic units the options are 0.03 meter cubic or 30000 centimeter cubic, not good units to have in a prose. – Luiz Borges Dec 17 '11 at 1:31
• I can't tell from the question exactly what you need to convey. If it's the approximate volume, 30 litres is good. If it's the size/shape, I think the best option is a cube 30cm on the side. If you just say 30cm cube I suspect many non-technical readers will conflate this with 30 cubic cm and hopelessly underestimate the amount. People are generally bad at volumes - if you ask how much a cubic foot of water weighs, most people give answers far less than the true value (over 62 pounds). – FumbleFingers Dec 17 '11 at 13:55
• True indeed, volumes can confuse the reader very easily... :( – Luiz Borges Dec 17 '11 at 14:19