The safest answer is to consult your preferred publisher's style guide; there may be differences of opinion on issues like this. https://physics.nist.gov/cuu/U

The safest answer is to consult your preferred publisher's style guide; there may be differences of opinion on issues like this. https://physics.nist.gov/cuu/Units/checklist.html https://physics.nist.gov/cuu/Units/checklist.html, for example, says (item #15): > There is a space between the numerical value and unit symbol ... (although they fail to recommend making it a non-breaking space, which I think would be wiser). There's plenty of further discussion to be found; e.g. https://forum.wordreference.com/threads/typography-rules-for-units-of-measurements.2781694/ https://forum.wordreference.com/threads/typography-rules-for...