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I want to know the most commonly understood meaning of phrases like "twice the size of" or "three times the size of" 3D objects.

If I say "this ball is twice the size of a table tennis ball", do native English speakers envision something with twice a table tennis' ball diameter? Or twice its volume? Or something else?

What about cubes?

What should I picture when someone describes an object using these kinds of descriptions?

  • You can picture whatever you want to picture, but you should really ask for clarification. – J.R. Apr 9 '18 at 21:01
  • Twice the size calls for knowing dimensions or volume. Cubes and 3D objects can be tiny or huge. Twice the size of the Earth, I can figure out. Twice the size of a cube=no idea. – Lambie Apr 9 '18 at 21:03
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    "Twice the size of the Earth" ... without clarification, that could easily mean "twice the surface area" (if we're talking about living space, for example) or "twice the volume" (if we're talking about gravitational pull), and it wouldn't be much of a stretch to suppose "twice the radius". That's the problem: You just don't know what the writer is thinking. – Jay Apr 9 '18 at 21:18
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    @WeatherVane - I think it's a fair learner's question. Sometimes most native speakers will agree that a word almost always means something; other times, it will be ambiguous. Learners should feel free to ask here and find out what the skinny is. – J.R. Apr 9 '18 at 21:54
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    Assuming this is asked of the average English speaker (whoever that is), in a non-technical context, I think size would be judged as visual size, basically a 2D view from the viewer's perspective. – user3169 Apr 9 '18 at 22:02
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It's ambiguous.

I think that if you say "twice the size" of a 3D object, that SHOULD mean twice the volume. But many people say that meaning "twice the diameter" or "twice the length of a side".

If you want to be clear, you should use different words.

Afterthought

I read a book on statistics once that talked about misleading presentations of statistics. One example they gave was a graph that purported to show differences in income between various groups. The graph had a picture of a money bag for each group. And the HEIGHT of the money bag was proportional to the income of that group, e.g. if group X made twice as much money as group Y, then group X's bag was twice as tall. But, the writer pointed out, this gave a very misleading impression, because the bag in the picture was two dimensional, and so if X's bag was twice as tall, it would be 4 times the area. And the bags depicted 3-dimenstional objects, so X's bag would be 8 times the volume. It exaggerated the differences tremendously.

  • I agree. Part of this stems from visual cues. It only takes a modest increase in the diameter of a sphere to double the volume of that sphere; so, if I said, "A basketball is roughly twice the size of a volleyball," that may be true mathematically, but it doesn't seem to mesh with what we see. – J.R. Apr 9 '18 at 20:52
  • @J.R. so can I assume from your comment that the common meaning is more like twice the diameter than twice the volume – theonlygusti Apr 9 '18 at 21:06
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    @theonlygusti - I'm telling you what crosses my mind. It's just a theory. I don't think anyone can definitively say what most people think, or what the "common meaning" is. – J.R. Apr 9 '18 at 21:24
  • I suspect that if you did a random survey of English speakers, most would assume doubling the radius of a sphere doubles the volume. Only a small percentage would guess more than 2x, and only a small percentage of those actually know the formula. So really it depends on the mathematical ability of the intended audience. – Andrew Apr 9 '18 at 22:34

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