Every now and then I come across a question that uses American units, which I am not familiar with. That's not a big deal, I simply use Google to convert everything to metric, and it only takes a few minutes.

I also agree with the general consensus here that it should not be a rule to post in any particular unit system, nor to provide conversions yourself when posting. (cf. others questions)

However, since in such cases I have done the conversions already, I might as well save a few minutes to the next persons who will read the post, or to myself if I return to it later. Hence I'm always tempted to edit along these lines

the monster is about 5ft tall and exactly 3.14ft wide. Its claws are 5-6 inches long

the monster is about 5ft tall [1.5 m] and exactly 3.14ft wide [0.957072 m]. Its claws are 5-6 inches long. [13-15 cm]

Would that be inappropriate, in the sense that it would be felt as if I'm correcting OP on something that was not required from them in the first place?

EDIT regarding the possible duplicate: two previous questions in asked if rules about units existed or were needed, one in general, and the other in the specific case of questions. The conclusions of both was not to impose any rule and let readers convert units. My question is different because it asks not about rules, but rather if that sort of editing would be considered welcome or rude.

  • $\begingroup$ Possible duplicate of Imperial vs. Metric System $\endgroup$
    – dot_Sp0T
    Commented Jan 12, 2019 at 19:31
  • $\begingroup$ not that I'm disagreeing with the answer you marked as accepted but maybe its a little early to accept an answer? (I mean it I've seen unit arguments get heated before esp. when precision is a factor) $\endgroup$ Commented Jan 13, 2019 at 2:20
  • $\begingroup$ @JGreenwell true, I unaccepted it for now. $\endgroup$
    – Alexis
    Commented Jan 13, 2019 at 9:08

5 Answers 5


When rejecting an edit, we need to justify the rejection through a dialog. It provides the following options:

spam or vandalism

This edit defaces the post in order to promote a product or service, or is deliberately destructive.

no improvement whatsoever

This edit does not make the post even a little bit easier to read, easier to find, more accurate or more accessible. Changes are either completely superfluous or actively harm readability.

clearly conflicts with author's intent

This edit deviates from the original intent of the post. Even edits that must make drastic changes should strive to preserve the goals of the post's owner.

attempt to reply

This edit was intended to address the author of the post and makes no sense as an edit. It should have been written as a comment or an answer.

causes harm

(Textbox for you to say why it causes harm)

Editing a post to add unit conversion falls in none of the above cases, so anyone who doesn't like the edit can go take a hike.

That kind of edit is appreciated as it adds clarity, and you are encouraged to do it through some badges. Also, until you reach 2,000 reputation, you'll be awarded 2 rep points per edit. So keep editing :)

  • 2
    $\begingroup$ "in nome of the above" -> should be "none of the above". Can't edit to fix this, so I guess, I'll go take a hike now $\endgroup$
    – VLAZ
    Commented Jan 14, 2019 at 15:07
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    $\begingroup$ @vlaz you can edit to fix typos and you are awarded for that ;) I always accept those edits on my posts when I'm alerted to them. $\endgroup$ Commented Jan 14, 2019 at 15:15
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    $\begingroup$ I would have done that but clicking "edit" on meta gives me "Suggested edits are not allowed on non-tag-wiki posts on meta sites." $\endgroup$
    – VLAZ
    Commented Jan 14, 2019 at 15:17
  • $\begingroup$ @vlaz I see. Sorry for that :( once you get to 2,000 rep you don't get that anymore, so please keep participating. $\endgroup$ Commented Jan 14, 2019 at 15:37

That's something I have done by myself various times, as jumping between the question and the converter is not so handy.

Since it is an integration and definitely improves clarity, especially in those cases where the number is highly meaningful to the question, I would see no reason to reject such an edit.


It is almost always appropriate to edit in unit conversion; and in both directions! If a query is in normal units, then editing to add metric is not only acceptable but commendable. Same goes for the other direction. If a query is in metric, an edit to put the numbers in normal units is perfectly fine. In my opinion, it should be a regular practice of the writer of good quality questions to do this as a matter of courteous habit.

There are only two exceptions I'd make to that rule:

  1. One exception to this is in a highly technical query. It's customary, even in the US, to do chemistry and physics and so forth in SI. A query about orbital mechanics that is full of equations and is completely in SI units of measure do not need to be translated into normal units in my opinion.
  2. The other exception is when an OP uses in-world units of measure without also offering a conversion factor. If I say a certain character dances the "thirty leuyves and three" between Endumion and Charedon, saying that's nearly a hundred miles, I would not accept a conversion into SI. Simply because I have not, for the purpose of the question, specified the conversion factor.

Precision in edited conversions is very important! I actually concur when it comes to matters of precision. If the OP says "approximately", then any edit that offers an approximate conversion is okay. If the OP says "exactly" or "precisely", then take that as a "hard science moment" and offer an exact & precise conversion as is warranted. This is not done for the sake of the OP, but for the sake of readers unfamiliar with the original units.

OP's original intent should not be violated. I also concur as to OP's intent. If an OP uses a particular system of measurement, for whatever reason as is their right, editing in a conversion is fine. But editors should be ware! Editors should never overwrite the OP's chosen system of measure for any reason.

I was recently "victimised" by a well meaning edit of this sort:

Is the Avian species from the game Starbound plausible?

I choose words very carefully, and used the word crore very intentionally. While I appreciate editing for clarity (and, perhaps, also in order to earn the editor's badge), sadly, when it got edited, the conversion got done wrong. (That's "putting words in the OP's mouth" in my book.) So I have to take the time to go back and re-edit the editor's edit so that what appears on the page is what I actually intend to say!

The take away lesson: when you edit, be very careful what you change! If I were reviewing that edit to my response, I'd probably reject it with a note to the editor that the conversion is wrong and would thus be unhelpful.

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    $\begingroup$ American units are not "normal". They are called "Standard units" or "Customary Units". Sometimes, the system is wrongly referred to as being "Imperial units". Metric is the normal unit for the majority of the world. I would recommend correcting this facet of your answer due to the implication it gives off that I don't think you intended to imply. I am saying this as a formality, so please don't mistake me for trying to be combative. I just think it's a good idea to be accurate when possible. $\endgroup$ Commented Jan 16, 2019 at 19:43

I've also added in conversions. Though only for questions I was editing anyway and in cases where I cared enough to look it up. I think it was just once actually but I was answering the question and needed to make those conversions so it would make sense inside my head (yes of course I know how to use metric, but it's not something I can feel). I used an online calculator and rounded only very slightly. I agree it's important to stick to the precision level the OP used.


It is inappropriate to add incorrect unit conversions.

If you are going to put words in the author's mouth, you need to make sure that they match the author's intent. At a minimum, any parenthetical notes need to be correct to the same number of significant figures as the author's original values.

The example proposed edit [was] wrong, even within the number of significant figures given. [The previous proposed edit said 0.95 meters.] "Exactly 3.14 feet" is 0.957 meters, or approximately 0.96 meters. The [previous] proposed edit therefore [needed to] either be further edited to match the author's intent, or be rejected as "clearly conflicts with author's intent".

  • 1
    $\begingroup$ @F1Krazy -- Stack Exchange gives many editors the ability to change the text attributed to an author without the author's knowledge. That is morally the same as "putting words in the author's mouth". $\endgroup$
    – Jasper
    Commented Jan 15, 2019 at 14:13
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    $\begingroup$ Regarding your last remark - well, that seems to be kinda nitpicky (and this is from someone who can admittedly be extremely nitpicky at times). "Clearly conflicts with the author's intent" is usually used as a rejection reason for edits that dramatically change the meaning of a paragraph or the answer as a whole, and I don't think using an uncommon rounding convention counts. Plus . . . I don't know. It's a single centimeter. The addition of the unit conversions is to make things more intuitive for folks who used that unit system. "0.95 m" and "0.96 m" both adequately convey that. $\endgroup$
    – HDE 226868 Mod
    Commented Jan 15, 2019 at 14:17
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    $\begingroup$ @HDE226868 -- Yes, it is a fine point. But the example used the word "exactly". $\endgroup$
    – Jasper
    Commented Jan 15, 2019 at 14:18
  • 1
    $\begingroup$ @Jasper Sure. And I think it would be prudent for the reviewer to hit "approve and edit" (which I think is maybe an underused feature?) rather than "reject" if that's the only issue; again, that's not really what "conflicts with the author's intent" is meant for. $\endgroup$
    – HDE 226868 Mod
    Commented Jan 15, 2019 at 14:19
  • $\begingroup$ @HDE226868 -- Yes, "Approve and edit" is appropriate. But notice that none of edits made by the posters in this comment thread go through the review queue. Technically, mine might, but won't after my reputation increases modestly. $\endgroup$
    – Jasper
    Commented Jan 15, 2019 at 14:21
  • $\begingroup$ @HDE226868 -- I have updated the answer to mention the further editing possibility. $\endgroup$
    – Jasper
    Commented Jan 15, 2019 at 14:30
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    $\begingroup$ Ah oops, you are perfectly right, sorry. That was indeed the intent of writing "exactly" in my example, to illustrate the same precision should be kept, and then I forgot about it when I wrote the edited example. $\endgroup$
    – Alexis
    Commented Jan 15, 2019 at 23:00
  • $\begingroup$ I have to disagree that unit conversions need to be to the same number of significant digits. For example if you are converting 1.01mm to inches, it is clear that the authors wants something way more precise than 0.04in. Because inches are so much bigger than mm. I would recommend, your conversion should be to the significant digit that rounds to the original number exactly when converted back which for this example would be 0.0397in. $\endgroup$
    – Nosajimiki
    Commented Feb 12, 2019 at 15:09
  • $\begingroup$ @Nosajimiki -- I agree with your conclusion. And the actual definition of significant figures tries as hard as it can to agree. For example, 1.01 mm and 0.0397 inches both have 3 significant figures. 0.04 inches only has 1 significant figure. $\endgroup$
    – Jasper
    Commented Feb 12, 2019 at 18:52

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