In cases where a physical quantity (consisting of a number and a unit) is used like an adjective to describe a property of an object, should it be written with or without a hyphen between the number and the unit?
- "A 2 kilogram potato" or "A 2-kilogram potato"?
- "We use 4 Gbit memory devices" or "We use 4-Gbit memory devices"?
Is one of the forms correct, or are both forms possible?
The second example is supposed to refer to an unspecified number of memory devices with 4 Gbit (gigabits, of capacity) each, rather than four memory devices.
Does any of the following modifications make difference?
- The quantity is written as a word instead of digits, i. e. "A two kilogram potato" vs. "A two-kilogram potato" ("two" instead of "2")
- The unit is abbreviated rather than written out, i. e. "A 2 kg potato" vs. "A 2-kg potato" ("kg" instead of "kilogram")
- The quantity is a decimal fraction, i. e. "A 1.5 kg potato" vs. "A 1.5-kg potato"
- The quantity is a simple fraction, i. e. "A 1/2 kg potato" vs. "A 1/2-kg potato"?
Furthermore, would it ever be correct to use a hyphen in a case like "This potato has a weight of 2-kg" (or "2-kilograms")?
An answer to this question (which discusses a different case) states that when there is no ambiguity, hyphens may be omitted. Does that statement apply to this case?